U.S. patent number 7,030,551 [Application Number 09/924,108] was granted by the patent office on 2006-04-18 for area sensor and display apparatus provided with an area sensor.
This patent grant is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Hajime Kimura, Jun Koyama, Shunpei Yamazaki, Yu Yamazaki, Masato Yonezawa.
United States Patent |
7,030,551 |
Yamazaki , et al. |
April 18, 2006 |
Area sensor and display apparatus provided with an area sensor
Abstract
An area sensor of the present invention has a function of
displaying an image in a sensor portion by using light-emitting
elements and a reading function using photoelectric conversion
devices. Therefore, an image read in the sensor portion can be
displayed thereon without separately providing an electronic
display on the area sensor. Furthermore, a photoelectric conversion
layer of a photodiode according to the present invention is made of
an amorphous silicon film and an N-type semiconductor layer and a
P-type semiconductor layer are made of a polycrystalline silicon
film. The amorphous silicon film is formed to be thicker than the
polycrystalline silicon film. As a result, the photodiode according
to the present invention can receive more light.
Inventors: |
Yamazaki; Shunpei (Tokyo,
JP), Koyama; Jun (Kanagawa, JP), Yonezawa;
Masato (Kanagawa, JP), Kimura; Hajime (Kanagawa,
JP), Yamazaki; Yu (Tokyo, JP) |
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd. (Atsugi, JP)
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Family
ID: |
18733867 |
Appl.
No.: |
09/924,108 |
Filed: |
August 8, 2001 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20020044208 A1 |
Apr 18, 2002 |
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Foreign Application Priority Data
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Aug 10, 2000 [JP] |
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2000-242932 |
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Current U.S.
Class: |
313/498; 257/53;
257/57; 257/E27.11; 257/E31.09; 257/E27.14; 257/72; 257/52;
257/E27.147; 257/E27.133; 348/E5.025; 348/E3.018 |
Current CPC
Class: |
H01L
27/3258 (20130101); H01L 27/3269 (20130101); H01L
29/78672 (20130101); H01L 27/14643 (20130101); H01L
27/3246 (20130101); H01L 27/3276 (20130101); H01L
27/3234 (20130101); H01L 51/0097 (20130101); H01L
27/3248 (20130101); H01L 27/15 (20130101); H04N
5/374 (20130101); H01L 27/14692 (20130101); H01L
27/3262 (20130101); H01L 27/3265 (20130101); H04N
3/155 (20130101); G09G 3/3266 (20130101); H01L
27/14632 (20130101); H01L 27/14678 (20130101); H01L
27/14623 (20130101); G09G 3/3258 (20130101); H01L
27/323 (20130101); H01L 27/14687 (20130101); G09G
2310/0286 (20130101); G09G 2320/0646 (20130101); G09G
2300/0809 (20130101); Y02E 10/549 (20130101); H01L
2251/5338 (20130101); G09G 2310/0291 (20130101); H01L
27/3244 (20130101) |
Current International
Class: |
H05B
33/08 (20060101) |
Field of
Search: |
;313/498
;257/E27.141,E25.112,52,53,E31.095,E31.096 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
US. Appl. No. 09/760,894, filed Jan. 17, 2001, Yamazaki et al.
cited by other .
Tsutsui et al.; "Electroluminescence in Organic Thin Films";
Photochemical Processes in Organized Molecular Systems; pp.
437-450; 1991. cited by other .
Baldo et al.; "Highly Efficient Phosphorescent Emission from
Organic Electroluminescent Devices"; Nature, vol. 395; pp. 151-154;
Sep. 10, 1998. cited by other .
Baldo et al.; "Very High-Efficiency Green Organic Light-Emitting
Devices Based on Electrophosphorescence"; Applied Physics Letters,
vol. 75(1); pp. 4-6; Jul. 5, 1999. cited by other .
Tsutsui et al; "High Quantum Efficiency in Organic Light-Emitting
Devices with Irdium-Comolex as a Triplet Emissive Center"; Japanese
Journal of Applied Physics, vol. 38, Part 12B; pp. L1502-L1504;
Dec. 15, 1999. cited by other .
W. A. Steer et al., AM-LCD '03, Digest of Technical Papers,
"Systems Aspects of Active-Matrix Polymer LED Displays," Jul. 9-11,
2003, Tokyo, Japan, pp. 285-288. cited by other.
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Primary Examiner: Santiago; Mariceli
Attorney, Agent or Firm: Fish & Richardson P.C.
Claims
What is claimed is:
1. An area sensor comprising a sensor portion, the sensor portion
comprising: a plurality of pixels, each of the plurality of pixels
comprising a photodiode, an electroluminescence element and a
plurality of thin film transistors, wherein: the photodiode
includes a photoelectric conversion layer that is in contact with a
part of a P-type semiconductor layer and an N-type semiconductor
layer, the photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
2. An area sensor according to claim 1, wherein the N-type
semiconductor layer comprises polysilicon.
3. An area sensor according to claim 1, wherein the P-type
semiconductor layer comprises polysilicon.
4. An area sensor according to claim 1, wherein the photoelectric
conversion layer comprises amorphous silicon.
5. An area sensor according to claim 1, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
6. An area sensor according to claim 1, wherein the area sensor is
included in electronic equipment selected from the group of: a
video camera, a digital still camera, a notebook computer and a
portable information terminal.
7. An area sensor comprising a sensor portion, the sensor portion
comprising: a plurality of pixels, each of the plurality of pixels
comprising a photodiode, an electroluminescence element and a
plurality of thin film transistors, wherein: light emitted from the
electroluminescence element is reflected from a subject to be
radiated to the photodiode, the photodiode generates an image
signal from the light reflected to the photodiode, the photodiode
includes a photoelectric conversion layer that is in contact with a
part of a P-type semiconductor layer an N-type semiconductor layer,
the photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
8. An area sensor according to claim 7, wherein the N-type
semiconductor layer comprises polysilicon.
9. An area sensor according to claim 7, wherein the P-type
semiconductor layer comprises polysilicon.
10. An area sensor according to claim 7, wherein the photoelectric
conversion layer comprises amorphous silicon.
11. An area sensor according to claim 7, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
12. An area sensor according to claim 7, wherein the area sensor is
included in electronic equipment selected from the group of: a
video camera, a digital still camera, a notebook computer and a
portable information terminal.
13. An area sensor comprising a sensor portion, the sensor portion
comprising: a plurality of pixels, each of the plurality of pixels
comprising a photodiode, an electroluminescence element and a
plurality of thin film transistors, wherein: the plurality of thin
film transistors control light emission of the electroluminescence
element, light emitted from the electroluminescence element is
reflected from a subject to be radiated to the photodiode, the
photodiode and the plurality of thin film transistors generate an
image signal from the light reflected to the photodiode, the
photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, the photoelectric conversion layer is made of
an amorphous semiconductor film, and the photoelectric conversion
layer is thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
14. An area sensor according to claim 13, wherein the N-type
semiconductor layer comprises polysilicon.
15. An area sensor according to claim 13, wherein the P-type
semiconductor layer comprises polysilicon.
16. An area sensor according to claim 13, wherein the photoelectric
conversion layer comprises amorphous silicon.
17. An area sensor according to claim 13, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
18. An area sensor according to claim 13, wherein the area sensor
is included in electronic equipment selected from the group of: a
video camera, a digital still camera, a notebook computer and a
portable information terminal.
19. An area sensor comprising a sensor portion, the sensor portion
comprising: a plurality of pixels, each of the plurality of pixels
comprising a photodiode, an electroluminescence element, a
switching TFT, an electroluminescence driving TFT, a reset TFT, a
buffer TFT and a selective TFT, wherein: the switching TET and the
electroluminescence driving TFT control light emission of the
electroluminescence element, light emitted from the
electroluminescence element is reflected from a subject to be
radiated to the photodiode, the photodiode and the plurality of
thin film transistors generate an image signal from the light
reflected to the photodiode, the photodiode includes a
photoelectric conversion layer that is in contact with a part of a
P-type semiconductor layer and an N-type semiconductor layer, the
photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
20. An area sensor according to claim 19, wherein the N-type
semiconductor layer comprises polysilicon.
21. An area sensor according to claim 19, wherein the P-type
semiconductor layer comprises polysilicon.
22. An area sensor according to claim 19, wherein the photoelectric
conversion layer comprises amorphous silicon.
23. An area sensor according to claim 19, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
24. An area sensor according to claim 19, wherein the area sensor
is included in electronic equipment selected from the group of: a
video camera, a digital still camera, a notebook computer and a
portable information terminal.
25. A display apparatus comprising a sensor portion, the sensor
portion comprising: a plurality of pixels, each of the plurality of
pixels comprising a photodiode, an electroluminescence element and
a plurality of thin film transistors, wherein: the photodiode
includes a photoelectric conversion layer that is in contact with a
part of a P-type semiconductor layer and an N-type semiconductor
layer, the photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
26. A display apparatus according to claim 25, wherein the N-type
semiconductor layer comprises polysilicon.
27. A display apparatus according to claim 25, wherein the P-type
semiconductor layer comprises polysilicon.
28. A display apparatus according to claim 25, wherein the
photoelectric conversion layer comprises amorphous silicon.
29. A display apparatus according to claim 25, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
30. A display apparatus according to claim 25, wherein the display
apparatus is included in electronic equipment selected from the
group of: a video camera, a digital still camera, a notebook
computer and a portable information terminal.
31. A display apparatus comprising a sensor portion, the sensor
portion comprising: a plurality of pixels, each of the plurality of
pixels comprising a photodiode, an electroluminescence element and
a plurality of thin film transistors, wherein: a light emitted from
the electroluminescence element is reflected from a subject to be
radiated to the photodiode, the photodiode generates an image
signal from the light reflected to the photodiode, the photodiode
includes a photoelectric conversion layer that is in contact with a
part of a P-type semiconductor layer and an N-type semiconductor
layer, the photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
32. A display apparatus according to claim 31, wherein the N-type
semiconductor layer comprises polysilicon.
33. A display apparatus according to claim 31, wherein the P-type
semiconductor layer comprises polysilicon.
34. A display apparatus according to claim 31, wherein the
photoelectric conversion layer comprises amorphous silicon.
35. A display apparatus according to claim 31, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
36. A display apparatus according to claim 31, wherein the display
apparatus is included in electronic equipment selected from the
group of: a video camera, a digital still camera, a notebook
computer and a portable information terminal.
37. A display apparatus comprising a sensor portion, the sensor
portion comprising: a plurality of pixels, each of the plurality of
pixels comprising a photodiode, an electroluminescence element and
a plurality of thin film transistors, wherein: the plurality of
thin film transistors control light emission of the
electroluminescence element, a light emitted from the
electroluminescence element is reflected from a subject to be
radiated to the photodiode, the photodiode and the plurality of
thin film transistors generate an image signal from the light
reflected to the photodiode, the photodiode includes a
photoelectric conversion layer that is in contact with a part of a
P-type semiconductor layer and an N-type semiconductor layer, the
photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
38. A display apparatus according to claim 37, wherein the N-type
semiconductor layer comprises polysilicon.
39. A display apparatus according to claim 37, wherein the P-type
semiconductor layer comprises polysilicon.
40. A display apparatus according to claim 37, wherein the
photoelectric conversion layer comprises amorphous silicon.
41. A display apparatus according to claim 37, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
42. A display apparatus according to claim 25, wherein the display
apparatus is included in electronic equipment selected from the
group of: a video camera, a digital still camera, a notebook
computer and a portable information terminal.
43. A display apparatus comprising a sensor portion, the sensor
portion comprising: a plurality of pixels, each of the plurality of
pixels comprising a photodiode, an electroluminescence element, a
switching TFT, an electroluminescence driving TFT, a reset TFT, a
buffer TFT and a selective TFT, wherein: the switching TFT and the
electroluminescence driving TFT control light emission of the
electroluminescence element, light emitted from the
electroluminescence element is reflected from a subject to be
radiated to the photodiode, the photodiode and the plurality of
thin film transistors generate an image signal from the light
reflected to the photodiode, the photodiode includes a
photoelectric conversion layer that is in contact with a part of a
P-type semiconductor layer and an N-type semiconductor layer, the
photoelectric conversion layer is made of an amorphous
semiconductor film, and the photoelectric conversion layer is
thicker than the P-type semiconductor layer and the N-type
semiconductor layer.
44. A display apparatus according to claim 43, wherein the N-type
semiconductor layer comprises polysilicon.
45. A display apparatus according to claim 43, wherein the P-type
semiconductor layer comprises polysilicon.
46. A display apparatus according to claim 43, wherein the
photoelectric conversion layer comprises amorphous silicon.
47. A display apparatus according to claim 43, wherein the
electroluminescence element has a positive electrode, a negative
electrode and an electroluminescence layer provided between the
positive electrode and the negative electrode.
48. A display apparatus according to claim 25, wherein the display
apparatus is included in electronic equipment selected from the
group of: a video camera, a digital still camera, a notebook
computer and a portable information terminal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an area sensor (semiconductor
device) having an image sensor function and a display function. In
particular, the present invention relates to an area sensor
(semiconductor device) that has EL (electroluminescence) elements
as a light source and is composed of photoelectric conversion
devices provided on a flat surface (insulating surface) and a
plurality of thin film transistors (TFTs) arranged in a matrix.
2. Description of the Related Art
In recent years, a solid-state image sensing device is being used,
which has diodes, CCDs, or the like for reading an electric signal
having image information from a light signal having
textural/graphic information, video information, and the like on a
sheet of paper. Such a solid-state image sensing device is used for
a scanner, a digital camera, and the like.
The solid-state image sensing device having photoelectric
conversion devices are classified into a line sensor and an area
sensor. In the line sensor, photoelectric conversion devices
provided in a line shape are scanned with respect to a subject,
whereby image information is captured as an electric signal.
The area sensor is also called a contact-type area sensor, in which
photoelectric conversion devices provided on a flat surface are
disposed on a subject, and image information is captured as an
electric signal. Unlike the line sensor, it is not required to scan
photoelectric conversion devices in the area sensor, so that a
motor and the like for scanning are not necessary.
FIGS. 23A and 23B show a configuration of a conventional area
sensor. FIG. 23A is a perspective view of the area sensor, and FIG.
23B is a cross-sectional view thereof. A sensor substrate 2501 with
photoelectric conversion devices formed thereon, a backlight 2502,
and a light scattering plate 2503 are provided as shown in FIG.
23B.
Light from the backlight 2502 (light source) is refracted in the
light scattering plate 2503, and is radiated to a subject 2504. The
radiated light is reflected from the subject 2504, and radiated to
the photoelectric conversion devices provided on the sensor
substrate 2501. When the photoelectric conversion devices are
irradiated with light, a current with a magnitude in accordance
with the brightness of light is generated in the photoelectric
conversion devices, and image information of the subject 2504 is
captured in the area sensor as an electric signal.
In the above-mentioned area sensor, when light is not radiated
uniformly to the subject from the backlight 2502, a read image may
partially become light or dark, resulting in inconsistencies of the
image. This makes it necessary to design the light scattering plate
2503 so that light is radiated uniformly to the subject 2504, and
to precisely adjust the position of the backlight 2502, the light
scattering plate 2503, the sensor substrate 2501, and the subject
2504.
It is also difficult to minimize the size of the backlight 2502 and
the light scattering plate 2503, which prevents the area sensor
from becoming small, thin, and light-weight.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the
present invention to provide an area sensor that is small, thin,
and light-weight, and in which a read image has no inconsistencies
in lightness.
An area sensor of the present invention uses a photodiode as a
photoelectric conversion device. The area sensor also uses an
electroluminescense (EL) element as a light source.
In the present specification, a photodiode (photoelectric
conversion device) includes an N-type semiconductor layer, a P-type
semiconductor layer, and a photoelectric conversion device provided
so as to come into contact with a part of the N-type semiconductor
layer and the P-type semiconductor layer.
When a photodiode is irradiated with light, the voltage thereof is
decreased due to carriers generated by the light. At this time, as
light intensity is higher, the amount of a decrease in voltage
becomes larger. Furthermore, by comparing a voltage in the case
where a photodiode is irradiated with light, with a voltage in the
case where the photodiode is not irradiated with light, a signal is
input to a sensor signal line.
An EL element (light-emitting element) is a spontaneous
light-emitting element, and is mainly used for an EL display. An EL
display is also called an organic EL display (OELD) or an organic
light-emitting diode (OLED).
An EL element has a configuration in which an EL layer (organic
compound layer) is interposed between a pair of electrodes
(positive electrode and negative electrode), and the EL layer
usually has a multi-layer configuration. Typically, there is a
multi-layer configuration "hole transport layer/light-emitting
layer/electron transport layer" proposed by Tang of Eastman Kodak.
This configuration has a very high light-emitting efficiency, and
most of the EL display apparatuses that are being studied and
developed adopt this configuration.
Alternatively, an EL layer may have a configuration in which a hole
injection layer, a hole transport layer, a light-emitting layer,
and an electron transport layer are stacked in this order on an
electrode or a configuration in which a hole injection layer, a
hole transport layer, a light-emitting layer, an electron transport
layer, and an electron injection layer are stacked in this order on
an electrode. A light-emitting layer may be doped with a
fluorescent colorant or the like.
In the present specification, all the layers provided between a
pair of electrodes are collectively referred to as an "EL layer
(organic compound layer)". Therefore, the above-mentioned hole
injection layer, hole transport layer, light-emitting layer,
electron transport layer, electron injection layer, etc. are all
included in the EL layer. A predetermined voltage is applied to an
EL layer with the above-mentioned configuration through a pair of
electrodes, whereby carriers are recombined in a light-emitting
layer to emit light.
In the present specification, an EL element (light-emitting
element) has a configuration in which an organic compound layer is
interposed between a pair of electrodes (positive electrode and
negative electrode). The organic compound layer can be made of a
known light-emitting material. Furthermore, the organic compound
layer can have a single-layer configuration and a multi-layer
configuration. According to the present invention the organic
compound layer may have either configuration. As luminescence in
the organic compound layer, there are light emission (fluorescence)
occurring when a singlet excited state is changed to a ground state
and light emission (phosphorescence) occurring when a triplet
excited state is changed to a ground state. According to the
present invention, either light emission may be used.
Photodiodes and EL elements are provided on the same sensor
substrate in a matrix. The photodiodes and the EL elements are
controlled for operation, respectively, using thin film transistors
(TFTs) similarly provided on the substrate in a matrix.
Light emitted from the EL elements is reflected from a subject and
radiated to the photodiodes. A current is generated by the light
radiated to the photodiodes, and an electric signal (image signal)
having image information of the subject is captured by an area
sensor.
According to the present invention, due to the above-mentioned
configuration, light is radiated uniformly to a subject, so that no
inconsistencies in lightness are caused in a read image.
Furthermore, it is not required to provide a backlight and a light
scattering plate separately from a sensor substrate. Therefore,
unlike a conventional example, an area sensor can be made small,
thin, and light-weight without precisely adjusting the position of
a backlight, a light scattering plate, a sensor substrate, and a
subject. Furthermore, the mechanical strength of an area sensor is
increased.
The area sensor of the present invention is also capable of
displaying an image, using the EL elements. The EL elements in the
present invention have a function as a light source for reading an
image and a function as a light source for displaying an image.
Therefore, even when an electronic display is not provided
separately on the area sensor, an image can be displayed.
Examples of a film made of silicon include a single crystal silicon
film, a polycrystalline silicon film (polysilicon film), an
amorphous silicon film (amorphous silicon film), etc. In the
photodiode according to the present invention, a photoelectric
conversion layer is made of an amorphous silicon film (amorphous
silicon film), an N-type semiconductor layer is made of an N-type
polycrystalline silicon film (polysilicon film), and a P-type
semiconductor layer is made of a polycrystalline silicon film
(polysilicon film). The amorphous silicon film is thicker than the
polycrystalline silicon film, and the ratio in thickness
therebetween is preferably (1 to 10):1. In the photodiode used in
the present invention, a photoelectric conversion layer can receive
more light when the thickness of the amorphous silicon film is
larger than that of the polycrystalline silicon film.
According to the present invention, a photoelectric conversion
layer is made of an amorphous silicon film due to its high light
absorptivity.
In a photodiode, a dark current (i.e., current flowing at a light
intensity of 0) may flow even when light is not radiated to the
photodiode. However, due to a high resistance of an amorphous
silicon film, a current does not flow even under the condition of
dark light, whereby a dark current can be decreased. More
specifically, when a dark current is small, a range of lightness
and darkness of light which a photodiode can receive is enlarged in
the case of dark light.
As shown in FIG. 16, a metal film 280 can also be formed so as to
cover a first interlayer insulating film 250 provided on a
photoelectric conversion layer 248.
Light is radiated to a subject 270 from an EL element, and light
reflected form the subject 270 is radiated to a photodiode 306.
However, in this case, among light passing through the photodiode
306, there exists light that is not radiated to the photoelectric
conversion layer 248. If the metal film 280 is present as shown in
FIG. 16, such light is reflected from the metal film 280, whereby
the photoelectric conversion layer 248 can receive it. Because of
this, the photoelectric conversion layer 248 can receive more
light.
Hereinafter, the constitution of the present invention will be
described.
According to the present invention, there is provided an area
sensor, characterized in that:
the sensor comprises a sensor portion provided with a plurality of
pixels each including a photodiode, an EL element, and a plurality
of thin film transistors;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided an area
sensor, characterized in that:
the sensor comprises a sensor portion provided with a plurality of
pixels each including a photodiode, an EL element, and a plurality
of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFY, an
EL driving TFT, a reset TFT, a buffer TFT, and a selective TFT;
the switching TFT and the EL driving TFT control light emission of
the EL element;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
the photodiode, the reset TFT, the buffer TFT, and the selective
TFT generate an image signal from the light radiated to the
photodiode;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided an area
sensor, characterized in that:
the area sensor comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line,
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode,
an image signal generated from the light radiated to the photodiode
is input to the sensor output line,
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film, and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided an area
sensor, characterized in that:
the area sensor comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
a polarity of the switching TFT is the same as that of the
selective TFT;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided an area
sensor, characterized in that:
the area sensor comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
the reset TFT and the selective TFT are switched from an ON state
to an OFF state or from an OFF state to an ON state by a signal
input to the reset gate signal line and the sensor gate signal
line;
when one of the reset TFT and the selective TFT is in an ON state,
the other is in an OFF state;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided an area
sensor, characterized in that:
the area sensor comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
a polarity of the switching TFT is the same as that of the
selective TFT;
the reset TFT and the selective TFT are switched from an ON state
to an OFF state or from an OFF state to an ON state by a signal
input to the reset gate signal line and the sensor gate signal
line;
when one of the reset TFT and the selective TFT is in an ON state,
the other is in an OFF state;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer and is made of an amorphous semiconductor film;
and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, and a selective TFT;
the switching TFT and the EL driving TFT controls light emission of
the EL element;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
the photodiode, the reset TFT, the buffer TFT, and the selective
TFT generate an image signal from the light radiated to the
photodiode;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer and is made of an amorphous semiconductor film;
and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
a polarity of the switching TFT is the same as that of the
selective TFT;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
the reset TFT and the selective TFT are switched from an ON state
to an OFF state or from an OFF state to an ON state by a signal
input to the reset gate signal line and the sensor gate signal
line;
when one of the reset TFT and the selective TFT is in an ON state,
the other is in an OFF state;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
According to the present invention, there is provided a display
device, characterized in that:
the display apparatus comprises a sensor portion provided with a
plurality of pixels each including a photodiode, an EL element, and
a plurality of thin film transistors;
the pixel includes a photodiode, an EL element, a switching TFT, an
EL driving TFT, a reset TFT, a buffer TFT, a selective TFT, a
source signal line, a gate signal line, a power supply line kept at
a constant potential, a reset gate signal line, a sensor gate
signal line, a sensor output line connected to a constant current
power source, and a sensor power source line kept at a constant
potential;
a gate electrode of the switching TFT is connected to the gate
signal line;
one of a source region and a drain region of the switching TFT is
connected to the source signal line, and the other is connected to
a gate electrode of the EL driving TFT;
a source region of the EL driving TFT is connected to the power
supply line, and a drain region of the EL driving TFT is connected
to the EL element;
a source region of the reset TFT is connected to the sensor power
source line;
a drain region of the reset TFT is connected to a gate electrode of
the buffer TFT and the photodiode;
a drain region of the buffer TFT is connected to the sensor power
source line;
one of a source region and a drain region of the selective TFT is
connected to the sensor output line, and the other is connected to
a source region of the buffer TFT;
a gate electrode of the selective TFT is connected to the sensor
gate signal line;
a polarity of the switching TFT is the same as that of the
selective TFT;
the reset TFT and the selective TFT are switched from an ON state
to an OFF state or from an OFF state to an ON state by a signal
input to the reset gate signal line and the sensor gate signal
line;
when one of the reset TFT and the selective TFT is in an ON state,
the other is in an OFF state;
light emitted from the EL element is reflected from a subject to be
radiated to the photodiode;
an image signal generated from the light radiated to the photodiode
is input to the sensor output line;
the photodiode includes a photoelectric conversion layer that is in
contact with a part of a P-type semiconductor layer and an N-type
semiconductor layer, and is made of an amorphous semiconductor
film; and
the photoelectric conversion layer is thicker than the P-type
semiconductor layer and the N-type semiconductor layer.
These and other advantages of the present invention will become
apparent to those skilled in the art upon reading and understanding
the following detailed description with reference to the
accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a circuit diagram of a sensor portion;
FIG. 2 is a circuit diagram of a pixel;
FIG. 3 is a timing chart of reading of an image in the sensor
portion;
FIG. 4 is a timing chart of reading of a color image in the sensor
portion;
FIG. 5 is a top view of an area sensor for digital driving;
FIG. 6 is a timing chart of light emission of an EL element when an
image is read;
FIG. 7 is a timing chart of light emission of an EL element when an
image is displayed;
FIG. 8 is a top view of an area sensor for analog driving;
FIG. 9 is a timing chart of light emission of an EL element when an
image is read;
FIGS. 10A to 10C show the steps of producing the sensor
portion;
FIGS. 11A to 11C show the steps of producing the sensor
portion;
FIGS. 12A to 12C show the steps of producing the sensor
portion;
FIGS. 13A to 13C show the steps of producing the sensor
portion;
FIGS. 14A and 14B show the steps of producing the sensor
portion;
FIG. 15 is an enlarged view of a photodiode according to the
present invention;
FIG. 16 is an enlarged view of a photodiode according to the
present invention;
FIGS. 17A and 17B are top views of the sensor portion of an area
sensor of the present invention;
FIGS. 18A to 18C show a schematic view and cross-sectional views of
the sensor portion of the area sensor of the present invention;
FIGS. 19A to 19C show the production steps according to the present
invention;
FIGS. 20A and 20B show the production steps according to the
present invention;
FIGS. 21A and 21B show an outer appearance of a portable hand
scanner that is an exemplary area sensor of the present
invention;
FIG. 22 shows an outer appearance of an area sensor provided with a
touch panel that is an exemplary area sensor of the present
invention;
FIGS. 23A and 23B are a perspective view and a cross-sectional view
of a conventional area sensor;
FIG. 24 is a circuit diagram of a sensor portion; and
FIGS. 25A to 25C show exemplary electronic equipment to which the
present invention is applicable.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the structure of an area sensor (semiconductor device)
of the present invention will be described. The area sensor of the
present invention includes a sensor portion for reading an image
and a driving portion for controlling driving of the sensor
portion. FIG. 1 shows a circuit diagram of the sensor portion
according to the present invention.
A sensor portion 101 is provided with source signal lines S.sub.1
to S.sub.x, power supply lines V.sub.1 to V.sub.x, gate signal
lines G.sub.1 to G.sub.y, reset gate signal lines RG.sub.1 to
RG.sub.y, sensor gate signal lines SG.sub.1 to SG.sub.y, sensor
output lines SS.sub.1 to SS.sub.x, and a sensor power source line
VB.
The sensor portion 101 has a plurality of pixels 102. Each pixel
102 includes one of the source signal lines S.sub.1 to S.sub.x, one
of the power supply lines V.sub.1 to V.sub.x, one of the gate
signal lines G.sub.1 to G.sub.y, one of reset the gate signal lines
RG.sub.1 to RG.sub.y, one of the sensor gate signal lines SG.sub.1
to SG.sub.y, one of the sensor output lines SS.sub.1 to SS.sub.x,
and the sensor power source line VB.
The sensor output lines SS.sub.1 to SS.sub.x are respectively
connected to constant current power sources 103.sub.--.sub.1 to
103.sub.--.sub.x.
FIG. 2 shows a detailed configuration of the pixel 102. A region
surrounded by a dotted line is the pixel 102. A source signal line
S denotes one of the source signal lines S.sub.1 to S.sub.x. A
power supply line V denotes one of the power supply lines V.sub.1
to V.sub.x. A gate signal line G denotes one of the gate signal
lines G.sub.1 to G.sub.y. A reset gate signal line RG denotes one
of the reset gate signal lines RG.sub.1 to RG.sub.y. A sensor gate
signal line SG denotes one of the sensor gate signal lines SG.sub.1
to SG.sub.y. A sensor output line SS denotes one of sensor output
lines SS.sub.1 to SS.sub.x.
The pixel 102 includes a switching TFT 104, an EL driving TFT 105,
and an EL element 106. In FIG. 2, although a capacitor 107 is
provided in the pixel 102, the capacitor 107 may not be
provided.
The EL element 106 is composed of a positive electrode, a negative
electrode, and an EL layer provided between the positive electrode
and the negative electrode. In the case where the positive
electrode is connected to a source region or a drain region of the
EL driving TFT 105, the positive electrode functions as a pixel
electrode and the negative electrode functions as a counter
electrode. In contrast, in the case where the negative electrode is
connected to a source region or a drain region of the EL driving
TFT 105, the positive electrode functions as a counter electrode
and the negative electrode functions as a pixel electrode.
A gate electrode of the switching TFT 104 is connected to the gate
signal line G. One of a source region and a drain region of the
switching TFT 104 is connected to the source signal line S, and the
other is connected to the gate electrode of the EL driving TFT
105.
The source region of the EL driving TFT 105 is connected to the
power supply line V, and the drain region of the EL driving TFT 105
is connected to the EL element 106. The capacitor 107 is provided
so as to be connected to the gate electrode of the EL driving TFT
105 and the power supply line V.
The pixel 102 further includes a reset TFT 110, a buffer TFT 111, a
selective TFT 112, and a photodiode 113.
A gate electrode of the reset TFT 110 is connected to the reset
gate signal line RG. A source region of the reset TFT 110 is
connected to the sensor power source line VB. The sensor power
source line VB is always kept at a constant electric potential
(reference potential). A drain region of the reset TFT 110 is
connected to the photodiode 113 and a gate electrode of the buffer
TFT 111.
Although not shown in the figure, the photodiode 113 has an N-type
semiconductor layer, a P-type semiconductor layer, and a
photoelectric conversion layer provided between the N-type
semiconductor layer and the P-type semiconductor layer. The drain
region of the reset TFT 110 is connected to either the P-type
semiconductor layer or the N-type semiconductor layer of the
photodiode 113.
A drain region of the buffer TFT 111 is connected to the sensor
power source line VB, and is always kept at a constant reference
potential. A source region of the buffer TFT 111 is connected to a
source region or a drain region of the selective TFT 112.
A gate electrode of the selective TFT 112 is connected to the
sensor gate signal line SG. One of a source region and a drain
region of the selective TFT 112 is connected to the source region
of the buffer TFT 111 as described above, and the other is
connected to the sensor output line SS. The sensor output line SS
is connected to the constant current power source 103 (one of the
constant current power sources 103.sub.--.sub.1 to
103.sub.--.sub.x), and is always supplied with a constant
current.
Hereinafter, a method for driving the area sensor of the present
invention will be briefly described with reference to FIGS. 1 and
2.
The EL element 106 of the pixel 102 functions as a light source of
the area sensor, and the switching TFT 104, the EL driving TFT 105,
and the capacitor 107 control the operation of the EL element 106
as a light source.
Light emitted from the EL element 106 is reflected from a subject,
and radiated to the photodiode 113 of the pixel 102. The photodiode
113 transforms the radiated light into an electric signal having
image information. The electric signal having image information
generated in the photodiode 113 is captured in the area sensor as
an image signal by the reset TFT 110, the buffer TFT 111, and the
selective TFT 112.
FIG. 3 is a timing chart showing the operation of the reset TFT
110, the buffer TFT 111, and the selective TFT 112. FIG. 3 shows a
timing chart in which the reset ITFT 110 is an N-channel type TFT,
the buffer TFT 111 is a P-channel type TFT, and the selective TFT
112 is an N-channel type TFT. According to the present invention,
the reset TFT 110, the buffer TFT 111, and the selective TFT 112
may be an N-channel type TFT or a P-channel type TFT. It is
preferable that the polarity of the reset TFT 110 is opposite to
that of the buffer TFT 111.
First, the reset TFTs 110 for pixels in the first line, connected
to the reset gate signal line RG.sub.1, are turned on with a reset
signal input to the reset gate signal line RG.sub.1. Then, the
reference potential of the sensor power source line VB is given to
the gate electrodes of the buffer TFTs 111.
The selective TFTs 112 for the pixels in the first line, connected
to the sensor gate signal line SG.sub.1 are turned off with a
sensor signal input to the sensor gate signal line SG.sub.1. Thus,
the source region of each buffer TFT 111 is kept at an electric
potential obtained by subtracting a potential difference VGS
between the source region and the gate region of the buffer TFT 111
from the reference potential. In the present specification, a
period during which the reset TFTs 110 are in an ON state is
referred to as a reset period.
Then, the electric potential of the reset signal input to the reset
gate signal line RG.sub.1 is changed, whereby all of the reset TFTs
110 for the pixels in the first line are turned off. As a result,
the reference potential of the sensor power source line VB is not
given to each gate electrode of the buffer TFTs 111 for the pixels
in the first line. In the present specification, a period during
which the reset TFTs 110 are in an OFF state is referred to as a
sampling period ST. In particular, a period during which the reset
TFTs 110 for the pixels in the first line are in an OFF state is
referred to as a sampling period ST.sub.1
During the sampling period ST.sub.1, the electric potential of the
sensor signal input to the sensor gate signal line SG.sub.1 is
changed, and the selective TFTs 112 for the pixels in the first
line are turned on. Thus, the source regions of the buffer TFTs 111
for the pixels in the first line are electrically connected to the
sensor output line SS.sub.1 via the selective TFTs 112. The sensor
output line SS.sub.1 is connected to the constant current power
sources 103.sub.--.sub.1. Therefore, each buffer TFT 111 functions
as a source follower, whereby the potential difference V.sub.GS
between the source region and the gate region of the buffer TFT 111
becomes constant.
When light emitted from the EL elements 106 is reflected from a
subject and radiated to the photodiodes 113 during the sampling
period ST.sub.1, a current flows through the photodiodes 113.
Therefore, the electric potential of the gate electrodes of the
buffer TFTs 111 kept at the reference potential during the reset
period is increased in accordance with the magnitude of a current
generated in the photodiodes 113.
A current flowing through each photodiode 113 is proportional to
the intensity of light radiated to the photodiode 113. Therefore,
image information of the subject is transformed to an electric
signal as it is by the photodiode 113. The electric signal
generated in the photodiode 113 is input to the gate electrode of
the buffer TFT 111.
The potential different V.sub.GS between the source region and the
gate region of the buffer TFT 111 is always kept constant.
Therefore, the source region of the buffer TFT 111 is kept at an
electric potential obtained by subtracting the potential difference
V.sub.GS from the electric potential of the gate electrode of the
buffer TFT 111. Consequently, when the electric potential of the
gate electrode of the buffer TFT 111 is changed, the electric
potential of the source region of the buffer TFT 111 is also
changed in accordance therewith.
The electric potential of the source region of the buffer TFT 111
is input of the sensor output line SS.sub.1 via the selective TFT
112 as an image signal.
Next, the reset TFTs 110 for the pixels in the first line,
connected to the reset gate signal line RG.sub.1, are turned on
with a reset signal input to the reset gate signal line RG.sub.1,
and a reset period is obtained again. Simultaneously, the reset
TFTs 110 for pixels in the second line, connected to the reset gate
signal line RG 2, are turned off with a reset signal input to the
reset gate signal line RG.sub.2, whereby a sampling period ST.sub.2
starts.
During the sampling period ST.sub.2, in the same way as in the
sampling period ST.sub.1, an electric signal having image
information is generated in the photodiodes, and an image signal is
input to the sensor output line SS.sub.2.
When the above-mentioned operation is repeated, and the sampling
period ST.sub.y is completed, one image can be read as an image
signal. In the present specification, a period during which all the
sampling periods ST.sub.1 to ST.sub.y are completed is referred to
as a sensor frame period SF.
During each sampling period, it is required to allow the EL element
of each pixel to emit light. For example, it is important that the
EL elements of the pixels in the first line emit light during at
least the sampling period ST.sub.1. All the pixels may emit light
during the sensor frame period SF.
In the case of an area sensor for reading a color image, a sensor
portion has pixels corresponding to red (R), green (G), and blue
(B) colors. Pixels corresponding to RGB colors have three kinds of
EL elements corresponding to RGB colors. Alternatively, they have
an EL element for emitting white light and three kinds of RGB color
filters. Alternatively they have an EL element for emitting blue
light or blue-green light and a phosphor (fluorescent color
transforming layer: CCM).
Light with RGB colors emitted from the pixels corresponding to RGB
colors is radiated to a subject successively. Light of each of RGB
colors reflected from the subject is radiated to photodiodes of the
pixels, and image signals corresponding to RGB colors are captured
in the area sensor.
FIG. 4 shows a timing chart showing the operation of the reset TFT
110, the buffer TFT 111, and the selective TFT 112 of the area
sensor for reading a color image. FIG. 4 shows a timing chart in
which the reset TFT 110 is an N-channel type TFT, the buffer TFT
111 is a P-channel type TFT, and the selective TFT 112 is an
N-channel type TFT.
While EL elements of pixels corresponding to R emit light, all the
sampling periods ST.sub.1 to ST.sub.y appear. A period during which
all the sampling periods ST.sub.1 to ST.sub.y are completed during
a period in which the EL elements of the pixels corresponding to R
emit light is referred to as an R sensor frame period SF.sub.r.
During the R sensor frame period SF.sub.r, an image signal
corresponding to R is captured in the area sensor. During the R
sensor frame SF.sub.r, pixels corresponding to G and B do not emit
light.
Next, while EL elements of the pixels corresponding to G emit
light, all the sampling periods TS.sub.1 to ST.sub.y appear. A
period during which all the sampling periods ST.sub.1 to ST.sub.y
are completed during a period in which the EL elements of the
pixels corresponding to G emit light is referred to as a G sensor
frame period SF.sub.g. During the G sensor frame period SF.sub.g,
an image signal corresponding to G is captured in the area sensor.
During the G sensor frame SF.sub.g, pixels corresponding to R and B
do not emit light.
Next, while EL elements of the pixels corresponding to B emit
light, all the sampling periods TS.sub.1 to ST.sub.y appear. A
period during which all the sampling periods ST.sub.1 to ST.sub.y
are completed during a period in which the EL elements of the
pixels corresponding to B emit light is referred to as a B sensor
frame period SF.sub.b. During the B sensor frame period SF.sub.b,
an image signal corresponding to B is captured in the area sensor.
During the B sensor frame SF.sub.b, pixels corresponding to R and G
do not emit light.
A period during which all the R sensor frame period SF.sub.r, the G
sensor frame period SF.sub.g, and the B sensor frame period
SF.sub.b are completed is a sensor frame period SF. When the sensor
frame period SF is completed, one color image can be read as an
image signal.
Furthermore, during each sampling period, it is required to allow
the EL elements of the pixels corresponding to each color to always
emit light. For example, during the sampling period ST.sub.1 in the
B sensor frame period, it is important that the EL elements of the
pixels corresponding to B among those in the first line always emit
light. Pixels corresponding to each color may always emit light
during each of the R, G, and B sensor frame period (SF.sub.r,
SF.sub.g, SF.sub.b).
According to the present invention, due to the above-mentioned
constitution, light is radiated uniformly to a subject. Therefore,
inconsistencies are not caused in lightness of a read image. It is
not required to provide a backlight and a light scattering plate
separately from a sensor substrate (i.e., substrate having an
insulating surface on which EL elements and photoelectric
conversion devices are provided). Therefore, unlike the
conventional example, an area sensor itself can be made small,
thin, and light-weight without precisely adjusting the position of
the backlight, the light scattering plate, the sensor substrate,
and the subject. The mechanical strength of the area sensor itself
is also increased.
Furthermore, the area sensor of the present invention is capable of
displaying an image in a sensor portion, using EL elements (light
source). Therefore, an image read by photodiodes can be displayed
in the sensor portion without separately providing an electronic
display on an area sensor, and a read image can be confirmed as
soon as it is read.
Embodiments
Hereinafter, the present invention will be described by way of
illustrative embodiments with reference to the drawings.
Embodiment 1
A method of driving the switching TFT 104 and the EL driving TFT
105, which control the operation of the EL element 106 shown in
FIG. 2, is explained in Embodiment 1. Note that the structure of
the sensor portion is the same as that of the embodiment mode, and
therefore FIG. 1 and FIG. 2 are referenced.
FIG. 5 shows a top view of an area sensor of Embodiment 1.
Reference numeral 120 denotes a source signal line driving circuit,
reference numeral 122 denotes a gate signal line driving circuit,
and both control the driving of the switching TFT 104 and the EL
driving TFT 105. Further, reference numeral 121 denotes a sensor
source signal line driving circuit, reference numeral 123 denotes a
sensor gate signal line driving circuit, and both control the
driving of the reset TFT 110, the buffer TFT 111, and the selection
TFT 112. Note that the source signal line driving circuit 120, the
gate signal line driving circuit 122, the sensor source signal line
driving circuit 121, and the sensor gate signal line driving
circuit 123 are referred to as a driving portion.
The source signal line driving circuit 120 has a shift register
120a, a latch (A) 120b, and a latch (B) 120c. A clock signal (CLK)
and a start pulse (SP) are inputted to the shift register 120a in
the source signal line driving circuit 120. The shift register 120a
generates timing signals in order based upon the clock signal (CLK)
and the start pulse (SP), and the timing signals are supplied one
after another to downstream circuits.
Note that the timing signals from the shift register 120a may be
buffer-amplified by a circuit such as a buffer (not shown in the
figure) and then supplied one after another to the downstream
circuits as the buffer-amplified timing signals. The load
capacitance (parasitic capacitance) of a wiring to which the timing
signals are supplied is large because many of the circuits and
elements are connected to the wiring. The buffer is formed in order
to prevent dullness in the rise and fall of the timing signal,
generated due to the large load capacitance.
The timing signals from the shift register 120a are supplied to the
latch (A) 120b. The latch (A) 120b has a plurality of latch stages
for processing a digital signal. The latch (A) 120b writes in and
maintains digital signals in order simultaneously with the input of
the timing signals.
Note that the digital signals may be sequentially inputted to the
plurality of latch stages of the latch (A) 120b when the digital
signals are taken in by the latch (A) 120b. However, the present
invention is not limited to this structure. A so-called division
drive may be performed, that is, the plurality of latch stages of
the latch (A) 120b is divided into a number of groups, and then the
digital signals are parallel inputted to the respective groups at
the same time. Note that the number of groups at this point is
called a division number. For example, if the latch circuits are
grouped into 4 stages each, then it is called a 4-branch division
drive.
The time necessary to complete writing of the digital signals into
all the latch stages of the latch (A) 120b is called a line period.
In other words, the line period is defined as a time interval from
the start of writing the digital data signals into the latch
circuit of the leftmost stage to the end of writing the digital
signals into the latch of the rightmost stage in the latch (A)
120b. In effect, the above-defined line period added with the
horizontal retrace period may also be referred to as the line
period.
After the completion of one line period, a latch signal is supplied
to the latch (B) 120c. In this moment, the digital signals written
in and held by the latch (A) 120b are sent all at once to the latch
(B) 120c to be written in and held by all the latch stages
thereof.
Sequential writing-in of digital signals on the basis of the timing
signals from the shift register 120a is again carried out to the
latch (A) 120b after it has completed sending the digital signals
to the latch (B) 120c.
During this second time one line period, the digital signals
written in and held by the latch (B) 120c are inputted to the
source signal lines S1 to Sx.
On the other hand, the gate signal line driving circuit 122 is
composed of a shift register and a buffer (both not shown in the
figure). Depending on the situation, the gate signal line driving
circuit 122 may have a level shifter in addition to the shift
register and the buffer.
In the gate signal line driving circuit 122, the gate signal is
supplied to the buffer (not shown in the figure) from the shift
register (also not shown in the figure), and this is supplied to a
corresponding gate signal line. Gate electrodes of the switching
TFTs 104 of one line portion of pixels are connected to each of the
gate signal lines G1 to Gy. All of the switching TFTs 104 of the
one line portion of pixels must be placed in an ON state
simultaneously, and therefore a buffer in which a large electric
current can flow is used.
Note that the number of source signal line driving circuits and
gate signal line driving circuits, their structure, and their
operation are not limited to the structure shown by Embodiment 1.
The area sensor of the present invention is capable of using a
known source signal line driving circuit and a known gate signal
line driving circuit.
Next, a timing chart for a case of driving the switching TFT 104
and the EL driving TFT 105 of the sensor portion by a digital
method is shown in FIG. 6.
A period through which all of the pixels of the sensor portion 101
emit light is referred to as one frame period F. The frame period
is divided into an address period Ta and a sustain period Ts. The
address period is a period in which a digital signal is inputted to
all of the pixels during one frame period. The sustain period (also
referred to as a turn-on period) denotes a period in which the EL
elements emit light or not in accordance with the digital signal
inputted to the pixels in the address period and display is
performed.
The electric potential of the electric power source supply lines V1
to Vx is maintained at a predetermined electric potential (electric
power source potential).
First, in the address period Ta, the electric potential of the
opposing electrode of the EL element 106 is maintained at the same
height as the electric power source potential.
Then all of the switching TFTs 104 connected to the gate signal
line G1 turn on in accordance with a gate signal inputted to the
gate signal line G1. A digital signal is next inputted from the
source signal line driving circuit 120 to the source signal lines
S1 to Sx. The digital signal inputted to the source signal lines S1
to Sx is inputted to the gate electrodes of the EL driving TFTs 105
through the switching TFTs 104 which are in an ON state.
Next, all of the switching TFTs 104 connected to the gate signal
line G2 are placed in an ON state in accordance with a gate signal
inputted to the gate signal line G2. The digital signal is then
inputted from the source signal line driving circuit 120 to the
source signal lines S1 to Sx. The digital signal inputted to the
source signal lines S1 to Sx is inputted to the gate electrodes of
the EL driving TFTs 105 through the switching TFTs 104 which are in
an ON state.
The above operations are repeated through the gate signal line Gy,
the digital signal is inputted to the gate electrodes of the EL
driving TFTs 105 of all the pixels 102, and the address period is
completed.
The sustain period begins simultaneously to the end of the address
period Ta. All of the switching TFTs 104 are placed in an OFF state
in the sustain period.
Then, at the same time as the sustain period begins, the electric
potential of the opposing electrodes of all the EL elements has a
height of the electric potential difference between the electric
power source potential to the level at which the EL elements will
emit light when the electric potential of the electric power source
is applied to the pixel electrodes. Note that the electric
potential difference between the pixel electrode and the opposing
electrode is referred to as an EL driving voltage in this
specification. Further, the EL driving TFTs 105 are placed in an ON
state in accordance with the digital signal inputted to the gate
electrode of the EL driving TFTs 105 of each pixel. Therefore, the
electric power source potential is applied to the pixel electrodes
of the EL elements, and the EL elements of all pixels emit
light.
One frame period is completed at the same time as the sustain
period is completed. It is necessary that the pixels emit light in
all of the sampling periods ST1 to STy with the present invention.
Therefore, it is very important that the sensor frame period SF be
included within the sustain period when using the digital driving
method of Embodiment 1.
Note that an explanation of a method of driving the area sensor for
reading in a single color image is explained in Embodiment 1, but a
case of reading in a color image is similar. However, for the case
of an area sensor which reads in a color image, one frame period is
divided into three subframe periods corresponding to RGB, and an
address period and a sustain period are formed in each subframe
period. A digital signal is inputted to all of the pixels such that
only the EL elements of pixels corresponding to R will emit light,
and only the EL elements for the color R perform light emission in
the sustain period. The subframe periods for G and B are similar,
and only EL elements of pixels corresponding to the respective
colors perform light emission in each sustain period.
For the case of an area sensor which reads in a color image, it is
important that each sustain period of the three subframe periods
corresponding to RGB contains a sensor frame period for R, G, and B
(SFr, SFg, SFb), respectively.
Embodiment 2
A method of driving the switching TFT 104 and the EL driving TFT
105 when displaying an image in the sensor portion 101 is explained
in Embodiment 2. Note that the structure of the sensor portion is
the same as the structure shown by the embodiment mode, and
therefore FIG. 1 and FIG. 2 may be referenced.
A timing chart when performing display of an image in the sensor
portion 101 in the area sensor of the present invention by a
digital method is shown in FIG. 7.
First, one frame period F is divided into N subframe periods SF1 to
SFN. The number of subframe periods in one frame period also
increases as the number of gray scales increases. Note that, when
the sensor portion of the area sensor displays an image, one frame
period F denotes a period during which all pixels of the sensor
portion display one image.
It is preferable that 60 or more frame periods be provided each
second for the case of Embodiment 2. By setting the number of
images displayed each second to 60 or greater, it becomes possible
to visually suppress image flicker.
The subframe period is divided into an address period Ta and a
sustain period Ts. The address period is a period within one
subframe period during which a digital video signal is inputted to
all pixels. Note that the digital video signal is a digital signal
having image information. The sustain period (also referred to as a
turn-on period) denotes a period during which EL elements are
placed in a state of emitting light or not emitting light in
accordance with the digital video signal inputted to the pixels in
the address period and display is performed. Note that the digital
video signal denotes the digital signal having image
information.
The address periods Ta of SF1 to SFN are taken as address periods
Ta1 to TaN, and the sustain periods Ts of SF1 to SFN are taken as
sustain periods Ts1 to TsN.
The electric potential of the electric power source supply lines V1
to Vx is maintained at a predetermined electric potential (electric
power source potential).
First, the electric potential of the opposing electrode of the EL
elements 106 is maintained at the same height as the electric power
source potential in the address period Ta.
Next, all of the switching TFTs 104 connected to the gate signal
line G1 are placed in an ON state in accordance with a gate signal
inputted to the gate signal line G1. The digital video signal is
then inputted to the source signal lines S1 to Sx from the source
signal line driving circuit 102. The digital video signal has "0"
or "1" information, and one of the "0" and "1" digital video
signals is a signal having a "HI" voltage, while the other is a
signal having a "LO" voltage.
The digital video signal inputted to the source signal lines S1 to
Sx is then inputted to the gate electrodes of the EL driving TFTs
105 through the switching TFTs 104 in an ON state.
All of the switching TFTs 104 connected to the gate signal line G1
are then placed in an OFF state, and all of the switching TFTs 104
connected to the gate signal line G2 are placed in an ON state in
accordance with a gate signal inputted to the gate signal line G2.
The digital video signal is then inputted to the source signal
lines S1 to Sx from the source signal line driving circuit 102. The
digital video signal inputted to the source signal lines S1 to Sx
is inputted to the gate electrodes of the EL driving TFTs 105
through the switching TFTs 104 in an ON state.
The above operations are repeated through the gate signal line Gy,
and the digital video signal is inputted to the gate electrodes of
the EL driving TFTs 105 of all the pixels 102, and the address
period is completed.
The sustain period Ts begins simultaneously with the completion of
the address period Ta. All of the switching TFTs 104 are in an OFF
state in the sustain period. The electric potential of the opposing
electrodes of all the EL elements has a height of the electric
potential difference between the electric power source potential to
the level at which the EL elements will emit light when the
electric potential of the electric power source is applied to the
pixel electrodes.
When the digital video signal has "0" information, the EL driving
TFT 105 is placed in an OFF state in Embodiment 2. The pixel
electrode of the EL elements is therefore maintained at the
electric potential of the opposing electrode. As a result, the EL
element 106 does not emit light when the digital video signal
having "0" information is inputted to the pixel.
On the other hand, when the digital video signal has "1"
information, the EL driving TFTs 105 are placed in an ON state. The
electric power source potential is therefore applied to the pixel
electrode of the EL element 106. As a result, the EL element 106 of
the pixel into which the digital video signal having "1"
information is inputted emits light.
The EL elements are thus placed in a state in which they emit light
or do not emit light in accordance with the information of the
digital video signal input to the pixels, and the pixels perform
display.
One subframe period is complete at the same time as the sustain
period is complete. The next subframe period then appears, and once
again the address period begins. The sustain period again beings
after the digital video signal is input to all of the pixels. Note
that the order of appearance of the subframe periods SF1 to SFn is
arbitrary.
Similar operations are then repeated in the remaining subframe
periods, and display is performed. After completing all of the n
subframe periods, one image is displayed, and one frame period is
completed. When one frame period is complete, the subframe period
of the next frame period appears, and the above stated operations
are repeated.
The lengths of the address periods Ta1 to Tan of the respective n
subframe periods are each the same in the present invention.
Further, the ratio of lengths of the n sustain periods Ts1, . . . ,
Tsn is expressed as Ts1:Ts2:Ts3: . . .
:Ts(n-1):Tsn=2.sup.0:2.sup.-1:2.sup.-2: . . .
:2.sup.-(n-2):2.sup.-(n-1).
The gray-scale of each pixel is determined in accordance with
during which subframe periods in one frame period the pixel is made
to emit light. For example, when n=8, and taking the brightness of
pixels which emit light in all of the sustain periods as having a
value of 100%, pixels which emit light in Ts1 and Ts2 can express a
brightness of 75%, and for a case of selecting Ts3, Ts5, and Ts8, a
brightness of 16% can be expressed.
Note that it is possible to freely combine Embodiment 2 with
Embodiment 1.
Embodiment 3
The electric potential of the opposing electrodes are maintained at
the same electric potential as that of the electric power source
potential during the address period in Embodiments 1 and 2.
Therefore, the EL elements do not emit light. However, the present
invention is not limited to this structure. If an electric
potential difference is always formed between the opposing electric
potential and the electric power source potential, on an order at
which the EL elements will emit light, when the electric power
source potential is applied to the pixel electrodes, display may
also be performed in the address period, similar to the display
period.
However, when combining Embodiment 1, in which the EL elements are
used as the light source of the area sensor, with Embodiment 3, it
is important that the sensor frame period SF be contained within
the frame period for an area sensor which reads in a single color
image. Furthermore, it is important that the three subframe periods
corresponding to RGB be contained in R, G, and B sensor frame
periods, respectively, for an area sensor which reads in a color
image.
In addition, when combining Embodiment 2, in which an image is
displayed in the sensor portion, with Embodiment 3, the entire
subframe period in practice becomes a period for performing
display, and therefore the lengths of the subframe periods are set
so as to be SF1:SF2:SF3: . . .
:SF(n-1):SFn=2.sup.0:2.sup.-1:2.sup.-2: . . .
:2.sup.-(n-2):2.sup.-(n-1). An image having a high brightness can
be obtained in accordance with the above structure when compared
with the drive method in which light is not emitted during the
address period.
Embodiment 4
An example of a method of driving the switching TFTs 104 and the EL
driving TFTs 105, which control the operation of the EL elements
106 shown in FIG. 2, by a method which differs from that of
Embodiment 1 is explained in Embodiment 4. Note that the structure
of the sensor portion is the same as that shown by the embodiment
mode, and therefore FIG. 1 and FIG. 2 may be referenced.
A top view of an area sensor of Embodiment 4 is shown in FIG. 8.
Reference numeral 130 denotes a source signal line driving circuit,
reference numeral 132 denotes a gate signal line driving circuit,
and both control the driving of the switching TFT 104 and the EL
driving TFT 105. Further, reference numeral 131 denotes a sensor
source signal line driving circuit, and reference numeral 133
denotes a sensor gate signal line driving circuit, and both control
the driving of the reset TFT 110, the buffer TFT 111, and the
selection TFT 112. One each of the source signal line driving
circuit and the gate signal line driving circuit are formed in
Embodiment 4, but the present invention is not limited to this
structure. Two source signal line driving circuits may also be
formed. Further, two gate signal line driving circuits may also be
formed.
Note that the source signal line driving circuit 130, the gate
signal line driving circuit 132, the sensor source signal line
driving circuit 131, and the sensor gate signal line driving
circuit 133 are referred to as a driving portion throughout this
specification.
The source signal line driving circuit 130 has a shift register
130a, a level shifter 130b, and a sampling circuit 130c. Note that
the level shifter may be used when necessary, and it need not
necessarily be used. Further, a structure is used in Embodiment 4
in which the level shifter is formed between the shift register
130a and the sampling circuit 130c, but the present invention is
not limited to this structure. A structure in which the level
shifter 130b is incorporated within the shift register 130a may
also be used.
A clock signal CLK and a start pulse signal SP are input to the
shift register 130a in the source signal line driving circuit 130.
A sampling signal is output from the shift register 130a in order
to sample an analog signal. The output sampling signal is input to
the level shifter 130b, and it electric potential amplitude is
increased, and it is output.
The sampling signal output from the level shifter 130b is input to
the sampling circuit 130c. The analog signal input to the sampling
circuit 130c is then sampled by the sampling signal, and input to
source signal lines S1 to Sx.
On the other hand, the gate signal line driving circuit 132 has a
shift register and a buffer (neither shown in the figure). Further,
the gate signal line driving circuit 132 may also have a level
shifter in addition to the shift register and the buffer, depending
upon the circumstances.
In the gate signal line driving circuit 132, a gate signal is
supplied to the buffer (not shown in the figure) from the shift
register (also not shown in the figure), and this is supplied to a
corresponding gate signal line. Gate electrodes of the switching
TFTs 104 of one line portion of pixels are connected to the gate
signal lines G1 to Gy, and all of the switching TFTs 104 of the one
line portion of pixels must be placed in an ON state
simultaneously, and therefore a buffer in which a large electric
current is capable of flowing is used.
Note that the number of source signal line driving circuits and
gate signal line driving circuits, their structure, and their
operation are not limited to the structure shown by Embodiment 4.
The area sensor of the present invention is capable of using a
known source signal line driving circuit and a known gate signal
line driving circuit.
Next, a timing chart for a case of driving the switching TFT 104
and the EL driving TFT 105 of the sensor portion by an analog
method is shown in FIG. 9. A period through which all of the pixels
of the sensor portion display light is referred to as one frame
period F. One line period L denotes a period from the selection of
one gate signal line until the selection of the next, separate,
gate signal line. For the case of the area sensor shown in FIG. 2,
there are y gate signal lines, and therefore y line periods L1 to
Ly are formed within one frame period.
The number of line periods within one frame period increases along
with increasing resolution, and the driving circuits must be driven
at a high frequency.
First, the electric potential of the electric power source supply
lines V1 to Vx is maintained at the constant electric power source
potential. The opposing electric potential, the electric potential
of the opposing electrodes of the EL elements 106, is also
maintained at a constant electric potential. The electric power
source potential has an electric potential difference with the
opposing electric potential on the order that the EL elements 106
will emit light when the electric power supply potential is applied
to the pixel electrodes of the EL elements 106.
In the first line period L1, all of the switching TFTs 104
connected to the gate signal line G1 are placed in an ON state in
accordance with a gate signal input to the gate signal line G1 from
the gate signal line driving circuit 132. The analog signal is then
input to the source signal lines S1 to Sx in order from the source
signal line driving circuit 130. The analog signal input to the
source signal lines S1 to Sx is input to the gate electrodes of the
EL driving TFTs 105 through the switching TFTs 104 which are in an
ON state.
The size of the electric current flowing in a channel forming
region of the EL driving TFTs 105 is controlled by the height of
the electric potential (voltage) of the signal input to the gate
electrodes of the EL driving TFTs 105. Therefore, the electric
potential applied to the pixel electrodes of the EL elements 106 is
determined by the height of the electric potential of the analog
signal input to the gate electrodes of the EL driving TFTs 105. The
EL elements 105 are controlled by the electric potential of the
analog signal, and perform the emission of light. Note that, in the
case of Embodiment 4, the analog signal input to all of the pixels
is maintained at an electric potential having the same height.
The first line period L1 is complete when input of the analog
signal to the source signal lines S1 to Sx is completed. Note that
the period until the input of the analog signal to the source
signal lines S1 to Sx is complete may also be combined with a
horizontal return period and taken as one line period. The second
line period L2 begins next, and all of the switching TFTs 104
connected to the gate signal line G1 are placed in an OFF state.
All of the switching TFTs 104 connected to the gate signal line G2
are then placed in an ON state in accordance with a gate signal
input to the gate signal line G2. Then, similar to the first line
period L1, the analog signal is input in order to the source signal
lines S1 to Sx.
The above operations are repeated up through the gate signal line
Gy, and all of the line periods L1 to Ly are complete. When all of
the line periods L1 to Ly are completed, one frame period is
complete. The EL elements of all of the pixels perform light
emission by completing one frame period. Note that all of the line
periods L1 to Ly and a vertical return period may also be combined
and taken as one frame period.
It is necessary for the pixels to emit light in all of the sampling
periods ST1 to STy with the present invention, and for the case of
the driving method of Embodiment 4, it is important that the sensor
frame period SF is included within the frame period.
Note that an explanation of a method of driving an area sensor for
reading in a single color image is explained in Embodiment 4, but a
case of reading in a color image is similar. However, for an area
sensor which reads in a color image, one frame period is divided
into three subframe periods corresponding to RGB. An analog signal
is then input to all of the pixels such that only the EL elements
of pixels corresponding to R will emit light in an R subframe
period, and only the EL elements for the color R perform light
emission. The subframe periods for G and B are similar, and only EL
elements of pixels corresponding to the respective color perform
light emission.
For the case of an area sensor which reads in a color image, it is
important that each sustain period of the three subframe periods
corresponding to RGB contain a sensor frame period for R, G, and B
(SFr, SFg, SFb), respectively.
Note that if an analog video signal having image information is
substituted for the analog signal for a case of displaying an image
in the sensor portion 101 in the driving method of Embodiment 4,
display of the image in the sensor portion 101 becomes
possible.
Embodiment 5
A cross sectional diagram of an area sensor of the present
invention is explained in Embodiment 5.
FIG. 14B shows a cross sectional diagram of an area sensor of
Embodiment 5. Reference numeral 301 denotes a switching TFT,
reference numeral 302 denotes an EL driving TFT, 303 denotes a
reset TFT, 304 denotes a buffer TFT, and reference numeral 305
denotes a selection TFT.
Further, reference numeral 242 denotes a p-type semiconductor
layer, 248 denotes a photoelectric conversion layer, and reference
numeral 238 denotes a n-type semiconductor layer. A photodiode 306
is formed by the p-type semiconductor layer 242, the photoelectric
conversion layer 248, and the n-type semiconductor layer 238.
Reference numeral 265 denotes a sensor wiring, and the sensor
wiring is connected the n-type semiconductor layer 238 and an
external electric power source. Further, the p-type semiconductor
layer 242 of the photodiode 306 and the drain region of the reset
TFT 303 is connected each other electrically.
Further, reference numeral 264 denotes a pixel electrode (anode),
266 denotes an EL layer and 267 denotes an opposing electrode
(cathode). An EL element 269 is formed by the pixel electrode
(anode) 264, the EL layer 266 and the opposing electrode (cathode)
267. Note that reference numeral 268 denotes a bank, and that the
EL layers 266 of adjacent pixels are separated.
Reference numeral 270 denotes a subject, and light emitted from the
EL element 269 is reflected by the subject 270 and is irradiated to
the photodiode 306. The subject 270 is formed on the side of a
sensor substrate 200 on which the TFTs are not formed in Embodiment
5.
The switching TFT 301, the buffer TFT 304, and the selection TFT
305 are all n-channel TFTs in Embodiment 5. Further, the EL driving
TFT 302 and the reset TFT 303 are a p-channel TFT. Note that the
present invention is not limited to this structure. Therefore, the
switching TFT 301, the EL driving TFT 302, the buffer TFT 304, the
selection TFT 305, and the reset TFT 303 may be either n-channel
TFTs or p-channel TFTs.
However, when a source region or a drain region of the EL driving
TFT 302 is electrically connected to the anode 264 of the EL
element 269, as in Embodiment 5, it is preferable that the EL
driving TFT 302 be a p-channel TFT. Conversely, when the source
region or the drain region of the EL driving TFT 302 is
electrically connected to the cathode of the EL element 269, it is
preferable that the EL driving TFT 302 be a n-channel TFT.
Note the photodiode and the other TFTs of Embodiment 5 can be
formed at the same time, and therefore the number of process steps
can be suppressed.
Note that it is possible to freely combine Embodiment 5 with
Embodiments 1 to 4.
Embodiment 6
A cross sectional diagram of an area sensor of the present
invention, differing from that of Embodiment 5, is explained in
Embodiment 6.
FIG. 15 shows a cross sectional diagram of an area sensor of
Embodiment 6. Reference numeral 701 denotes a switching TFT,
reference numeral 702 denotes an EL driving TFT, 703 denotes a
reset TFT, 704 denotes a buffer TFT, and reference numeral 705
denotes a selection TFT.
Further, reference numeral 738 denotes a n-type semiconductor
layer, 748 denotes a photoelectric conversion layer, and reference
numeral 742 denotes a p-type semiconductor layer. A photodiode 706
is formed by the n-type semiconductor layer 738, the photoelectric
conversion layer 748, and the p-type semiconductor layer 742.
Reference numeral 765 denotes a sensor wiring, and the sensor
wiring electrically connects the p-type semiconductor layer 742 and
an external electric power source. Further, the n-type
semiconductor layer 738 of the photodiode 706 and a drain region of
the reset TFT 703 are electrically connected.
Reference numeral 767 denotes a pixel electrode (cathode), 766
denotes an EL layer, and 764 denotes an opposing electrode (anode).
An EL element 769 is formed by the pixel electrode (cathode) 767,
the EL layer 766, and the opposing electrode (anode) 764. Note that
reference numeral 768 denotes a bank, and that the EL layers 766 of
adjacent pixels are separated.
Reference numeral 770 denotes a subject, and light emitted from the
EL element 769 is reflected by the subject 770 and is irradiated to
the photodiode 706. Differing from Embodiment 5, the subject 770 is
formed on the side of a substrate 700 on which the TFTs are formed
in Embodiment 6.
The switching TFT 701, the EL driving TFT 702, and the reset TFT
703 are all n-channel TFTs in Embodiment 6. Further, the buffer TFT
and the selection TFT are p-channel TFTs. Note that the present
invention is not limited to this structure. Therefore, the
switching TFT 701, the EL driving TFT 702, the buffer TFT 704, the
selection TFT 705, and the reset TFT 703 may be either n-channel
TFT's or p-channel TFTs.
However, when a source region or a drain region of the EL driving
TFT 702 is electrically connected to the cathode 709 of the EL
element 769, as in Embodiment 6, it is preferable that the EL
driving TFT 702 be a n-channel TFT. Conversely, when the source
region or the drain region of the EL driving TFT 702 is
electrically connected to the anode 712 of the EL element 769, it
is preferable that the EL driving TFT 702 be a p-channel TFT.
Furthermore, when the drain region of the reset TFT 703 is
electrically connected to the p-type semiconductor layer 742 of the
photodiode 706, as in Embodiment 6, it is preferable that the reset
TFT 703 be a n-channel TFT, and that the buffer TFT 704 be a
p-channel TFT. Conversely, when the drain region of the reset TFT
703 is electrically connected to the p-type semiconductor layer 742
of the photodiode 702, and the sensor wiring 765 is connected to
the n-type semiconductor layer 738, it is preferable that the reset
TFT 703 be a p-channel TFT, and that the buffer TFT 704 be a
n-channel TFT.
Note the photodiode 706 and the other TFTs of Embodiment 6 can be
formed at the same time, and therefore the number of process steps
can be suppressed.
Note also that it is possible to freely combine Embodiment 6 with
Embodiments 1 to 5.
Embodiment 7
A method of producing a sensor portion of an area sensor of the
present invention will be described with reference to FIGS. 10A to
14B. The sensor portion has switching TFTs 301, EL driving TFTs
302, reset TFTs 303, buffer TFTs 304, selective TFTs 305, and
diodes 306 on the same substrate.
First, referring to FIG. 10A, a substrate 200 made of glass such as
barium bolosilicate glass and aluminobolosilicate glass (e.g.,
#7059 glass and #1737 glass produced by Corning) is used in this
embodiment. The substrate 200 is not particularly limited as long
as it has light transparency. A quartz substrate, a glass
substrate, a ceramic substrate, or the like may be used.
Furthermore, a plastic substrate may be used, which has heat
resistance that can withstand a treatment temperature in this
embodiment.
As the substrate 200, a stainless substrate may be used. However,
since a stainless substrate is not transparent, it is effective
only when an EL element 769 emits light upward as shown in FIG.
15.
An insulating film (underlying film) made of silicon oxide is
formed on the substrate 200 so as to cover it. The insulating film
can be made of a silicon oxide film, a silicon nitride film, or a
silicon oxide nitride film. For example, a silicon oxide nitride
film made of SiH.sub.4, NH.sub.3, and N.sub.2O may be formed to a
thickness of 250 to 800 nm (preferably, 300 to 500 nm) by plasma
CVD. Similarly, a hydrogenated silicon oxide nitride film made of
SiH.sub.4 and N.sub.2O may be formed to a thickness of 250 to 800
nm (preferably, 300 to 500 nm). In this embodiment, an insulating
film made of silicon oxide is formed to a thickness of 250 to 800
nm so as to have a single-layer configuration. A material for the
insulating film is not limited to silicon oxide.
Next, a flattening insulating film 201 is formed by polishing the
insulating film by a CMP method. The CMP method is conducted by a
known method. In polishing an oxide film, slurry of a solid-liquid
dispersion system is generally used, in which an abrasive of 100 to
1000 nm.phi. is dispersed in an aqueous solution containing a
reagent such as a pH regulator. In this embodiment, silica slurry
(pH=10 to 11) is used, in which 20% by weight of fumed silica
particles obtained by thermally dissolving silicon chloride gas in
an aqueous solution with potassium hydroxide added thereto are
dispersed.
After the flattening insulating film 201 is formed, semiconductor
layers 202 to 208 are formed thereon. The semiconductor layers 202
to 208 are obtained by forming a semiconductor film having an
amorphous structure by a known method (e.g., sputtering, LPCVD,
plasma CVD, or the like), crystallizing the semiconductor film by
known crystallization process (e.g., laser crystallization, thermal
crystallization, thermal crystallization using a catalyst such as
nickel, or the like) to obtain a crystalline semiconductor film,
and patterning the crystalline semiconductor film to a desired
shape. The semiconductor layers 202 to 208 are formed to a
thickness of 25 to 80 nm (preferably, 30 to 60 nm). Although there
is no particular limit to a material for the crystalline
semiconductor film, a silicon or silicon germanium
(Si.sub.xGe.sub.1-x) alloy may be preferably used. In this
embodiment, an amorphous silicon film of 55 nm is formed by plasma
CVD, and thereafter, a solution containing nickel is held onto the
amorphous silicon film. After the amorphous silicon film is
dehydrogenated at 500.degree. C. for one hour, the film is
thermally crystallized at 550.degree. C. for four hours.
Furthermore, the amorphous silicon film is subjected to laser
annealing for the purpose of enhancing crystallization, whereby a
crystalline silicon film is formed. The crystalline silicon film is
patterned by photolithography to form the semiconductor layers 202
to 208.
After the semiconductor layers 202 to 208 are formed, they may be
doped with a trace amount of an impurity element (boron or
phosphorus) so as to control the threshold values of TFTs.
In the case of producing a crystalline semiconductor film by laser
crystallization, a pulse-oscillation type or continuous
light-emitting type excimer laser, a YAG laser, and a YVO.sub.4
layer can be used. In the case of using these lasers, a laser beam
emitted from a laser oscillator may be condensed in a line shape by
an optical system and radiated to a semiconductor film. Conditions
of crystallization are appropriately selected by those skilled in
the art. However, in the case of using an excimer laser, a pulse
oscillation frequency is set to be several 300 Hz, and a laser
energy density is set to be 100 to 400 mJ/cm.sup.2 (typically, 200
to 300 mJ/cm.sup.2). Furthermore, in the case of using a YAG laser,
the second harmonic thereof may be used, with a pulse oscillation
frequency set at several 30 to 300 kHz, and a laser energy density
set at 300 to 600 mJ/cm.sup.2 (typically 350 to 500 mJ/cm.sup.2).
Then, laser beams condensed in a line shape with a width of 100 to
1000 .mu.m (e.g., 400 .mu.m) may be radiated to the entire surface
of a substrate with an overlapped ratio of the line-shaped laser
beams set at 50% to 98%.
Then, a gate insulating film 209 covering the semiconductor layers
202 to 208 is formed. The gate insulating film 209 is formed of an
insulating film containing silicon with a thickness of 40 to 150 nm
by plasma CVD or sputtering. In this embodiment, a silicon oxide
nitride film (composition ratio: Si=32%, O=59%, N=7%, H=2%) is
formed to a thickness of 110 nm by plasma CVD. Needless to say, the
gate insulating film is not limited to a silicon oxide nitride
film. Another insulating film containing silicon may be used as a
single-layer or multi-layer configuration.
In the case of using a silicon oxide film as the insulating film,
the insulating film can be formed by mixing tetraethyl
orthosilicate (TEOS) and O.sub.2 by plasma CVD, setting a reaction
pressure at 40 Pa and a substrate temperature at 300.degree. C. to
400.degree. C., and allowing discharge to occur at a high-frequency
(13.56 MHz) power density of 0.5 to 0.8 W/cm.sup.2. The silicon
oxide film thus produced is subjected to thermal annealing at
400.degree. C. to 500.degree. C., thereby exhibiting satisfactory
characteristics as the gate insulating film.
Then, as shown in FIG. 10A, a first conductive film 210a
(thickness: 20 to 100 nm) and a second conductive film 210b
(thickness: 100 to 400 nm) are, stacked on the gate insulating film
209. In this embodiment, the first conductive film 210a made of a
TaN film with a thickness of 30 nm and the second conductive film
210b made of a W film with a thickness of 370 nm are stacked. The
TaN film is formed by sputtering using Ta as a target in a nitrogen
atmosphere. The W film is formed by sputtering using W as a target.
The W film can also be formed by thermal CVD, using tungsten
hexafluoride (WF.sub.6). In any case, the W film needs to have a
low resistance so as to be used as a gate electrode, and the
resistance of the W film is desirably 20 .mu..OMEGA.cm or less. By
enlarging crystal particles, the W film is allowed to have a low
resistance. However, in the case where a number of impurity
elements such as oxygen are present in the W film, crystallization
of the W film is inhibited to have a high resistance. Thus, in this
embodiment, the W film is formed by sputtering using W with a high
purity (99.9999%) as a target in such a manner that impurities are
not mixed from a vapor phase during film formation, whereby the
resistance of 9 to 20 .mu..OMEGA.cm of the W film can be
realized.
In this embodiment, although the first conductive film 210a is made
of TaN, and the second conductive film 210b is made of W, there is
no particular limit to the materials. The first and second
conductive films 210a and 210b may be made of an element selected
from Ta, W, Ti, Mo, Al, Cu, Cr, and Nd, or an alloy material or a
compound material containing the element as a main component.
Furthermore, a semiconductor film such as a polycrystalline silicon
film doped with an impurity element such as phosphorus may be used.
An AgPdCu alloy may also be used. Furthermore, it may be possible
that the first conductive film is made of a tantalum (Ta) film, and
the second conductive film is made of a W film. It may also be
possible that the first conductive film is made of a titanium
nitride (TiN) film, and the second conductive film is made of a W
film. It may also be possible that the first conductive film is
made of tantalum nitride (TaN) film, and the second conductive film
is made of an Al film. It may also be possible that the first
conductive film is made of a tantalum nitride (TaN) film, and the
second conductive film is made of a Cu film.
Next, a mask 211 made of a resist is formed by photolithography,
and first etching process for forming electrodes and wiring is
conducted (FIG. 10B). The first etching process is conducted under
first and second etching conditions. In this embodiment, under the
first etching condition, an inductively coupled plasma (ICP)
etching method is used, CF.sub.4, Cl.sub.2, and O.sub.2 are used as
etching gas, a gas flow ratio thereof is set at 25/25/10 (sccm),
and a coil-shaped electrode is supplied with an RF (13.56 MHz)
power of 500 W under a pressure of 1 Pa to generate plasma, whereby
etching is conducted. The substrate side (sample stage) is also
supplied with an RF (13.56 MHz) power of 150 W, whereby a
substantially negative self-bias voltage is applied. The W film is
etched under the first etching condition, thereby forming tapered
portions in a first conductive layer. An etching speed with respect
to W under the first etching condition is 200.39 nm/min, and an
etching speed with respect to TaN is 80.32 nm/min, and a selection
ratio of W with respect to TaN is about 2.5. Furthermore, the taper
angle of W becomes about 26.degree. under the first etching
condition.
In the first etching process, by forming the mask 211 made of a
resist in an appropriate shape, the ends of the first conductive
layer and the second conductive layer are tapered due to the effect
of the bias voltage applied to the substrate side. The angle of the
tapered portion may be 15.degree. to 45.degree.. Thus, first-shaped
conductive layers 212 to 216 composed of first conductive layers
212a to 216a and second conductive layers 212b to 216b are formed
by the first etching process. Reference numeral 217 denotes a gate
insulating film, and regions not covered with the first-shaped
conductive layers 212 to 216 are etched by about 20 to 50 nm,
whereby thin regions are formed.
Then, second etching process is conducted without removing the mask
made of a resist (FIG. 10C). Herein, CF.sub.4, Cl.sub.2, and
O.sub.2 are used as etching gas, a gas flow ratio thereof is set at
25/25/10 (sccm), and a coil-shaped electrode is supplied with an RF
(13.56 MHz) power of 500 W under a pressure of 1 Pa to generate
plasma, whereby etching is conducted. The substrate side (sample
stage) is also supplied with an RF (13.56 MHz) power of 20 W,
whereby a substantially negative self-bias voltage is applied. An
etching speed with respect to W in the second etching process is
124.62 nm/min, and an etching speed with respect to TaN is 20.67
nm/min, and a selection ratio of W with respect to TaN is about
6.05. Thus, the W film is selectively etched. The taper angle of W
obtained by second etching becomes about 70.degree.. During the
second etching process, second conductive layers 218b to 222b are
formed. On the other hand, the first conductive layers 212a to 216a
are hardly etched to form first conductive layers 218a to 222a.
Reference numeral 223 denotes a gate insulating film, and regions
not covered with second-shaped conductive layers 218 to 222 are
etched by about 20 to 50 nm, whereby thin regions are formed.
An electrode formed of the first conductive layer 218a and the
second conductive layer 218b will become an N-channel type buffer
TFT 304 in the late step, and an electrode formed of the first
conductive layer 219a and the second conductive layer 219b will
become an N-channel type selective TFT 305 in the later step.
Similarly, an electrode formed of the first conductive layer 220a
and the second conductive layer 220b will become a P-channel type
reset TFT 303 in the later step, an electrode formed of the first
conductive layer 221a and the second conductive layer 221b will
become an N-channel type switching TFT 301 in the later step, and
an electrode formed of the first conductive layer 222a and the
second conductive layer 222b will become a P-channel type EL
driving TFT 302 in the later step.
Then, first doping process is conducted to obtain a state in FIG.
11A. Doping is conducted using the second conductive layers 218b to
222b as a mask with respect to an impurity element, in such a
manner that the impurity element is added to the semiconductor
layers below the taper portions of the first conductive layers 218a
to 222a. There is no conductive layer above the semiconductor
layers 205 and 206, so that these semiconductor layers are doped
from above the gate insulating film 223. In this embodiment, plasma
doping is conducted using phosphorus as an impurity element at a
dose amount of 3.5.times.10.sup.12 and an accelerating voltage of
90 keV. Thus, low-concentration impurity regions 224a to 228a, 229,
and 230 not overlapped with the first conductive layers, and
low-concentration impurity regions 224b to 228b overlapped with the
first conductive layers are formed in a self-alignment manner. The
concentration of phosphorus added to the low-concentration impurity
regions 224b to 228b is 1.times.10.sup.17 to 1.times.10.sup.18
atoms/cm.sup.3, and has a gentle concentration gradient along the
thickness of the taper portions of the first conductive layers 218a
to 222a. In the semiconductor layers overlapped with the taper
portions of the first conductive layers 218a to 222a, although the
impurity concentration is slightly decreased from the ends of the
taper portions of the first conductive layers 218a to 222a, the
concentration is substantially the same.
A mask 231 made of a resist is formed, and second doping process is
conducted, whereby an impurity element providing an N-type to the
semiconductor layers is added (FIG. 11B). Doping may be conducted
by ion doping or ion implantation. Ion doping is conducted under
the conditions of a dose amount of 1.times.10.sup.13 to
5.times.10.sup.15 atoms/cm.sup.2, and an acceleration voltage of 60
to 100 keV. In this embodiment, doping is conducted at a dose
amount of 1.5.times.10.sup.15 atoms/cm.sup.2 and an acceleration
voltage of 80 keV. As an impurity element providing an N-type, an
element belonging to the Group-XV, typically, phosphorus (P) or
arsenic (As) is used. Herein, phosphorus (P) is used. In this case,
the conductive layers 218 to 222 function as a mask with respect to
the impurity element providing an N-type, whereby
high-concentration impurity regions 232a to 236a, 237, and 238,
low-concentration impurity regions 232b to 236b not overlapped with
the first conductive layers, and low-concentration impurity regions
232c to 236c overlapped with the first conductive layers are formed
in a self-alignment manner. The high-concentration impurity regions
232a to 236a, 237, and 238 are supplied with an impurity element
providing an N-type in a concentration range of 1.times.10.sup.20
to 1.times.10.sup.21 atoms/cm.sup.3.
It is not required that the semiconductor films to be a P-channel
type are doped with an N-type impurity in the second doping process
shown in FIG. 11B. Therefore, the mask 231 may be formed so as to
completely cover the semiconductor layers 204, 206, and 208,
thereby preventing the semiconductor layers 204, 206, and 208 from
being doped with an N-type impurity. Alternatively, the mask 231 is
not provided above the semiconductor layers 204, 206 and 208, and
the polarity thereof may be reversed in third doping process.
Then, the mask 231 made of a resist is removed, and a mask 239 made
of a resist is newly formed to conduct third doping process.
Because of the third doping process, impurity regions 240a to 240c,
241a to 241c, and 242 are formed, in which an impurity element
providing a conductivity (P-type) opposite to the above-mentioned
conductivity (N-type) is added to the semiconductor layers to be
active layers of P-channel type TFTs (FIG. 11C). The first
conductive layers 220b and 222b are used as a mask with respect to
an impurity element, and an impurity element providing a P-type is
added to form impurity regions in a self-alignment manner. There of
no conductive layer above the impurity region 242, so that the
impurity region 242 is doped from above the gate insulating film
223. In this embodiment, the impurity regions 240a to 240c, 241a to
241c, and 242 are formed by ion doping using diborane
(B.sub.2H.sub.6). During the third doping process, the
semiconductor layers to form N-channel type TFTs are covered with
the mask 239 made of a resist. During the first and second doping
process, the impurity regions 240a, 240b, and 240c are supplied
with phosphorus in different concentrations. However, by conducting
doping so that the concentration of the impurity element providing
a P-type becomes 2.times.10.sup.20 to 2.times.10.sup.21
atoms/cm.sup.3 in any region, there is no problem for these regions
to function as source regions and drain regions of P-channel type
TFTs.
Then, the impurity element added to the respective semiconductor
layers is activated. Activation is conducted by thermal annealing
using an annealing furnace. Thermal annealing may be conducted in a
nitrogen atmosphere with an oxygen concentration of 1 ppm or less
(preferably, 0.1 ppm or less) at 400.degree. C. to 700.degree. C.
(typically, 500.degree. C. to 550.degree. C.). In this embodiment,
activation is conducted by heat treatment at 550.degree. C. for
four hours. In addition to thermal annealing, laser annealing or
rapid thermal annealing (RTA method) can be applied.
Furthermore, activation may be conducted after forming a first
interlayer insulating film. In the case where a wiring material
used for wiring is weak to heat, it is preferable to conduct
activation after forming an interlayer insulating film (insulating
film mainly containing silicon, e.g., silicon nitride film) in
order to protect wiring and the like, as in this embodiment.
Furthermore, heat treatment is conducted at 300.degree. C. to
550.degree. C. for 1 to 12 hours in an atmosphere containing 3% to
100% hydrogen, whereby the semiconductor layers are hydrogenated.
In this embodiment, heat treatment is conducted at 410.degree. C.
for one hour in a nitrogen atmosphere containing about 3% hydrogen.
In this step, unpaired connecting ends of the semiconductor layers
are terminated with thermally excited hydrogen. As another
hydrogenation means, there is plasma hydrogenation (using hydrogen
excited with plasma).
Furthermore, hydrogenation may be conducted after a passivation
film is formed.
During the above-mentioned steps, impurity regions are formed in
the respective semiconductor layers.
Then, the mask 239 made of a resist is removed to conduct third
etching process. In this embodiment, using the conductive layers
218 to 222 as a mask, the gate insulating film is etched.
Because of the third etching process, gate insulating films 243c to
247c are formed under the second conductive layers 243b to 247b
(FIG. 12A).
Then, a passivation film 271 is formed so as to cover the substrate
200 (FIG. 12B). The passivation film 271 can be made of a silicon
oxide film, a silicon nitride film, or a silicon oxide nitride
film. For example, a silicon oxide nitride film made of SiH.sub.4,
NH.sub.3, and N.sub.2O may be formed to a thickness of 10 to 800 nm
(preferably, 50 to 500 nm) by plasma CVD. Similarly, a hydrogenated
silicon oxide nitride film made of SiH.sub.4 and N.sub.2O may be
formed to a thickness of 50 to 800 nm (preferably, 10 to 500 nm).
In this embodiment, the passivation film made of nitrogen oxide is
formed to a thickness of 10 to 800 nm with a single-layer
configuration.
Then, a mask 272 made of a resist is formed by photolithography,
and fourth etching process for forming an amorphous silicon film
248 is conducted. The resist mask 272 is formed so as to cover the
substrate, and to come into contact with a part of the P-type
semiconductor layer 242 and the N-type semiconductor layer 238
(FIG. 12C). Then, only the silicon nitride film is etched. In this
embodiment, ICP etching is used, CF.sub.4, Cl.sub.2, and O.sub.2
are used as etching gas, a gas flow ratio is set at 40/60/35
(sccm), and a coil-shaped electrode is supplied with an RF (13.56
MHz) power of 500 W under the pressure of 1 Pa to generate plasma,
whereby etching is conducted.
Then, the mask 272 made of a resist is removed. An amorphous
silicon film 248 is formed between the N-type semiconductor layer
242 and the P-type semiconductor layer 238 so as to come into
contact with a part of the N-type semiconductor layer 242 and the
P-type semiconductor layer 238 (FIG. 13A). The semiconductor film
having an amorphous structure is formed by a known method (e.g.,
sputtering, LPCVD, plasma CVD, or the like). The amorphous silicon
film 248 is formed to a thickness, preferably one to ten times that
of the N-channel type semiconductor layer 242 and the P-channel
type semiconductor layer 238. In this embodiment, the amorphous
silicon film 248 is formed to a thickness of 25 to 800 nm. Although
there is no particular limit to a material for the crystalline
semiconductor film, it may be preferably formed of silicon or a
silicon germanium (Si.sub.xGe.sub.1-x) alloy. In this embodiment,
after an amorphous silicon film with a thickness of 55 nm is formed
by plasma CVD, a solution containing nickel is held onto the
amorphous silicon film.
Then, a first interlayer insulating film 235 is formed (FIG. 13B).
The first interlayer insulating film 235 is obtained by forming an
insulating film containing silicon to a thickness of 100 to 200 nm
by plasma CVD or sputtering. In this embodiment, a silicon oxide
nitride film with a thickness of 150 nm is formed by plasma CVD.
Needless to say, the first interlayer insulating film 235 is not
limited to a silicon oxide nitride film. Another insulating film
containing silicon may be formed as a single-layer or multi-layer
configuration.
Then, the first interlayer insulating film 249 is patterned so as
to form contact holes reaching the impurity regions 232a, 233a,
235a, 238, 240a, 241a, and 242.
Then, source lines 251 to 256, and drain lines 257 to 262 are
formed. In this embodiment, as these lines, a film mainly
containing Al or Ag, or a material having excellent reflectivity
such as a layered film thereof are desirably used.
Then, as shown in FIG. 14A, a second interlayer insulating film 249
is formed. By using resin such as polyimide, polyamide,
polyimideamide, and acrylic resin, the second interlayer insulating
film 249 can have a flat surface. In this embodiment, a polyimide
film with a thickness of 0.7 .mu.m is formed over the entire
surface of the substrate as the second interlayer insulating film
249.
Next, as shown in FIG. 14B, a bank 268 made of a resin material is
formed. The bank 268 may be formed by patterning an acrylic film or
a polyimide film with a thickness of 1 to 2 .mu.m. The bank 268 may
be formed along the source line 256 or the gate line (not shown).
The bank 268 may be used as a shielding film by mixing a pigment or
the like in the resin material forming the bank 268.
Then, an EL layer 266 is formed. More specifically, an organic EL
material to be the EL layer 266 dissolved in a solvent such as
chloroform, dichloromethane, xylene, toluene, tetrahydrofuran, and
the like is applied, and thereafter, the solvent is vaporized by
heat treatment. Thus, a coating (EL layer) made of an organic EL
material is formed.
In this embodiment, only one pixel is shown. However, a
light-emitting layer emitting red light, a light-emitting layer
emitting green light, and a light-emitting layer emitting blue
light are formed simultaneously with the formation of the EL layer.
In this embodiment, as the light-emitting layer emitting red light,
cyanopolyphenylenevinylene is formed to a thickness of 50 nm.
Similarly, as the light-emitting layer emitting green light,
polyphenylenevinylene is formed to a thickness of 50 nm, and as the
light-emitting layer emitting blue light, polyalkylphenylene is
formed to a thickness of 50 nm. Furthermore, 1,2-dichloromethane is
used as a solvent, and the solvent is vaporized by heat treatment
with a hot plate at 80.degree. C. to 150.degree. C. for 1 to 5
minutes.
In this embodiment, although the EL layer has a single-layer
configuration, a hole injection layer, a hole transport layer, an
electron injection layer, an electron transport layer, and the like
may be additionally provided. Various examples of combinations have
already been reported, and any configuration may be used.
After the EL layer 266 is formed, a positive electrode 267 made of
a transparent conductive film is formed to a thickness of 120 nm as
a counter electrode. In this embodiment, a transparent conductive
film is used, in which 10 to 20% by weight of zinc oxide is added
to indium oxide. The positive electrode 267 is preferably formed by
vapor deposition at room temperature so as not to degrade the EL
layer 266.
As described above, the buffer TFT 304, the selective TFT 305, the
reset TFT 303, the diode 306, the switching TFT 301, the EL driving
TFT 302, and the EL element 269 can be formed on the same
substrate.
In this embodiment, Embodiments 1 to 5 can be arbitrarily
combined.
Embodiment 8
In a method of producing a sensor portion of the area sensor of the
present invention, a method of producing a photodiode different
from that in Embodiment 6 will be described with reference to FIG.
16.
FIG. 16 is an enlarged view of a photodiode 306. As shown in FIG.
16, in the photodiode 306, a metal film 280 is formed on a first
interlayer insulating film 250. The metal film 280 can be formed
simultaneously with formation of a source line 254 and a drain line
260. As the metal film 280, a film mainly containing Al or Ag that
is the same material as that of the lines, or a material having
excellent reflectivity such as a compound film thereof is desirably
used.
Light is radiated to a subject 270 from an EL element, and light
reflected form the subject 270 is radiated to the photodiode 306.
However, in this case, among light passing through the photodiode
306, there exists light that is not radiated to a photoelectric
conversion layer 248. If the metal film 280 is present as shown in
FIG. 16, such light is reflected from the metal film 280, whereby
the photoelectric conversion layer 248 can receive it. Because of
this, the photoelectric conversion layer 248 can receive more
light.
In this embodiment, Embodiments 1 to 7 can be arbitrarily
combined.
Embodiment 9
In this embodiment, an exemplary EL display apparatus
(light-emitting apparatus) produced according to the present
invention will be described with reference to FIGS. 17A 17B and 18A
18C.
FIG. 17A is a top view of a TFT substrate of an EL display
apparatus of the present invention. In the present specification,
the TFT substrate refers to the one on which a pixel portion is
provided.
A pixel portion 4002, a source signal line driving circuit 4003a
for a sensor, a source signal line driving circuit 4003b for an EL
element, a gate signal line driving circuit 4004a for an EL
element, and a gate signal line driving circuit 4004b for a sensor
are provided on a substrate 4001. According to the present
invention, the number of the source signal line driving circuits
and the gate signal line driving circuits are not limited to those
shown in FIG. 17A. The number of the source signal line driving
circuits and the gate signal line driving circuits can be
appropriately set by a designer. In this embodiment, although the
source signal line driving circuits and the gate signal line
driving circuits are provided on the TFT substrate, the present
invention is not limited thereto. The source signal line driving
circuits and the gate signal line driving circuits provided on a
substrate separate from the TFT substrate may be electrically
connected to the pixel portion via FPCs or the like.
Reference numeral 4005 denotes drawing-around wiring connected to a
power supply line (not shown) provided in the pixel portion 4002.
Reference numeral 4005 also denotes drawing-around wiring for a
gate connected to the gate signal line driving circuit 4004a for a
sensor and the gate signal line driving circuit 4004b for a gate.
Reference numeral 4005 also denotes drawing-around wiring for a
source connected to the source signal line driving circuit 4003a
for a sensor and the source signal line driving circuit 4003b for
an EL element.
The drawing-around wiring 4005 for a gate and the drawing-around
wiring 4005 for a source are connected to an IC and the like
provided outside of the substrate 4001 via the FPCs 4006. The
drawing-around wiring 4005 is also connected to a power source
provided outside of the substrate 4001 via the FPCs 4006.
FIG. 17B shows an enlarged view of the drawing-around wiring 4005.
Reference numeral 4100 denotes drawing-around wiring for R, 4101
denotes drawing-around wiring for G, and 4102 denotes
drawing-around wiring for B.
FIG. 18A shows a top view of an area sensor formed by sealing the
TFT substrate shown in FIG. 17A with a sealant. FIG. 18B shows a
cross-sectional view taken along a line A A' in FIG. 18A, and FIG.
18C shows a cross-sectional view taken along a line B B' in FIG.
18A. The same components as those shown in FIGS. 17A and 17B are
denoted with the same reference numerals as those therein.
A sealant 4009 is provided so as to surround the pixel portion
4002, the source signal line driving circuit 4003a for a sensor,
the source signal line driving circuit 4003b for an EL element, the
gate signal line driving circuit 4004a for a sensor, and the gate
signal line driving circuit 4004b for an EL element formed on the
substrate 4001. Furthermore, a sealing member 4008 is provided
above the pixel portion 4002, the source signal line driving
circuit 4003a for a sensor, the source signal line driving circuit
4003b for an EL element, the gate signal line driving circuit 4004a
for a sensor, and the gate signal line driving circuit 4004b for an
EL element. Thus, the pixel portion 4002, the source signal line
driving circuit 4003a for a sensor, the source signal line driving
circuit 4003b for an EL element, the gate signal line driving
circuit 4004a for a sensor, and the gate signal line driving
circuit 4004b for an EL element are sealed with the substrate 4001,
the sealant 4009, and the sealing member 4008, using a filler
4210.
Furthermore, the pixel portion 4002, the source signal line driving
circuit 4003a for a sensor, the source signal line driving circuit
4003b for an EL element, the gate signal line driving circuit 4004a
for a sensor, and the gate signal line driving circuit 4004b for an
EL element provided on the substrate 4001 have a plurality of TFTs.
FIG. 18B typically shows driving TFTs (herein, an N-channel type
TFT and a P-channel type TFT are shown) 4201 included in the source
signal line driving circuit 4003, and an EL driving TFT (i.e., TFT
for controlling a current to an EL element) and a photodiode 4211
included in the pixel portion, formed on a base film 4010.
In this embodiment, as the driving TFT 4201, a P-channel type TFT
or an N-channel type TFT produced by a known method is used. As the
EL driving TFT 4202, a P-channel type TFT produced by a known
method is used. Furthermore, in the pixel portion 4002, a retention
capacitance (not shown) connected to a gate of the EL driving TFT
4202 is provided.
An interlayer insulating film (flattening film) 4301 is formed on
the driving TFT 4201, the EL driving TFT 4202, and the photodiode
4211. A pixel electrode (positive electrode) 4203 electrically
connected to a drain of the EL driving TFT 4202 is formed on the
interlayer insulating film 4301. As the pixel electrode 4203, a
transparent conductive film with a large work function is used. As
the transparent conductive film, a compound of indium oxide and tin
oxide, a compound of indium oxide and zinc oxide, zinc oxide, tin
oxide, or indium oxide can be used. Furthermore, gallium may be
added to the transparent conductive film.
On the pixel electrode 4203, an insulating film 4302 is formed. The
insulating film 4302 has an opening in a portion corresponding to
the pixel electrode 4203. In this opening, an EL layer 4204 is
formed on the pixel electrode 4203. As the EL layer 4204, a known
organic EL material or an inorganic EL material can be used. There
are a low-molecular type (monomer type) material and a
high-molecular type (polymer type) material as the organic EL
material. Either material may be used.
The EL layer 4204 may be formed by a known vapor deposition
technique or a coating technique. Furthermore, the EL layer may
have a multi-layer configuration or a single-layer configuration by
arbitrarily combining a hole injection layer, a hole transport
layer, a light-emitting layer, an electron transport layer, or an
electron injection layer.
On the EL layer 4204, a negative electrode 4205 made of a
conductive film (typically, conductive film mainly containing
aluminum, copper, or silver, or a layered film composed of this
conductive film and another conductive film) having a light
shielding property is formed. Furthermore, it is desirable to
exclude moisture and oxygen present on an interface between the
negative electrode 4205 and the EL layer 4204 as much as possible.
Thus, it is required to form the EL layer 4204 in an atmosphere of
nitrogen or noble gas, and to form the negative electrode 4205
without bringing it into contact with oxygen and moisture. In this
embodiment, the above-mentioned film-formation is possible by using
a film-formation apparatus of a multi-chamber system (cluster-tool
system). The negative electrode 4205 is supplied with a
predetermined voltage.
As described above, an EL element 4303 composed of the pixel
electrode (positive electrode) 4203, the EL layer 4204, and the
negative electrode 4205 is formed. Then, a protective film 4209 is
formed on the insulating film 4302 so as to cover the EL element
4303. The protective film 4209 is effective for preventing oxygen,
moisture, and the like from entering the EL element 4303.
Reference numeral 4005 denotes drawing-around wiring connected to a
power supply line, which is electrically connected to a source
region of the EL driving TFT 4202. The drawing-around wiring 4005
extends between the sealant 4009 and the substrate 4001, and is
electrically connected to wiring 4301 of the FPCs via an
anisotropic conductive film 4300.
As the sealing member 4008, a glass material, a metal material
(typically, a stainless material), a ceramics material, and a
plastic material (including a plastic film) can be used. As the
plastic material, a fiberglass-reinforced plastic (FRP) plate, a
polyvinyl fluoride film (PVF), a myler film, a polyester film, or
an acrylic resin film can be used. Furthermore, a sheet having a
configuration in which an aluminum foil is interposed between a PVF
film and a myler film can also be used.
In the case where light is radiated from an EL element toward a
cover member side, the cover member must be transparent. In this
case, a transparent material, such as a glass plate, a plastic
plate, a polyester film, or an acrylic film, is used for the cover
member.
As the filler 4210, UV-curable resin or thermosetting resin, as
well as inert gas such as nitrogen and argon, can be used. More
specifically, polyvinyl chloride (PVC), acrylic resin, polyimide,
epoxy resin, silicon resin, polyvinyl butyral (PVB), or
ethylenevinyl acetate (EVA) can be used. In this embodiment,
nitrogen is used as the filler.
In order to expose the filler 4210 to a moisture-absorbing material
(preferably, barium oxide) or an oxygen-adsorbing material, a
concave portion 4007 is provided on the surface of the sealing
member 4008 on the substrate 4001 side, and a moisture-absorbing
material or an oxygen-adsorbing material 4207 is disposed therein.
The moisture-absorbing material or oxygen-adsorbing material 4207
is held in the concave portion 4007 by a concave portion cover
member 4208 so as not to scatter. The concave portion cover member
4208 has a fine mesh shape which transmits air and moisture but
does not transmit the moisture-absorbing material or the
oxygen-adsorbing material 4207. By providing the moisture-absorbing
material or the oxygen-adsorbing material 4207, the EL element 4303
can be prevented from being degraded.
As shown in FIG. 18C, a conductive film 4203a is formed so as to
come into contact with the drawing-around wiring 4005a,
simultaneously with the formation of the pixel electrode 4203.
Furthermore, the anisotropic conductive film 4300 contains a
conductive filler 4300a. By thermally crimping the substrate 4001
onto the FPC 4006, the conductive film 4203a on the substrate 4001
and the wiring 4301 for an FPC on the FPC 4006 are electrically
connected to each other via the conductive filler 4300a.
In this embodiment, Embodiments 1 to 7 can be arbitrarily
combined.
Embodiment 10
In this embodiment, the case will be described with reference to
FIGS. 19A to 19C, in which TFTs and EL elements are sealed onto a
substrate with a sealing member, and thereafter, the substrate is
replaced. FIGS. 19A to 19C are cross-sectional views showing the
steps of producing a pixel portion.
In FIG. 19A, reference numeral 3101 denotes a substrate
(hereinafter, referred to as a "device forming substrate") on which
devices are to be formed. On the substrate 3101, a peeling layer
3102 made of an amorphous silicon film is formed to a thickness of
100 to 500 nm (300 nm in this embodiment). In this embodiment,
although a glass substrate is used as the device forming substrate
3101, a quartz substrate, a silicon substrate, a metal substrate
(SUS substrate), or a ceramic substrate may be used.
The peeling layer 3102 may be formed by thermal CVD under reduced
pressure, plasma CVD, sputtering, or vapor deposition. On the
peeling layer 3102, an insulating film 3103 is made of a silicon
oxide film having a thickness of 200 nm. The insulating film 3103
may be formed by thermal CVD under reduced pressure, plasma CVD,
sputtering, or vapor deposition.
Furthermore, photodiodes 3104 and EL driving TFTs 3105 are formed
on the insulating film 3103. In this embodiment, although the EL
driving TFTs 3105 are P-channel type TFTs, the present invention is
not limited thereto. The EL driving TFTs 3105 may be P-channel type
TFTs or N-channel type TFTs.
A first interlayer insulating film 3107 is formed on the
photodiodes 3104 and the EL driving TFTs 3105. The first interlayer
insulating film 3107 is formed covering the photodiodes 3104 and
the EL driving TFTs 3105, so as to flatten pixel electrodes 3106
(formed later).
Each pixel electrode 3106 is formed so as to be electrically
connected to a drain region of the EL driving TFT 3105. In this
embodiment, the pixel electrode 3106 is obtained by forming a
transparent conductive film (typically, a compound film of indium
oxide and tin oxide) having a thickness of 100 nm, followed by
patterning. The pixel electrode 3106 functions as a positive
electrode of an EL element.
After the pixel electrodes 3106 are formed, a second interlayer
insulating film 3114 made of a silicon oxide film with a thickness
of 300 nm is formed. Openings 3108 are formed in the second
interlayer insulating film 3114, and EL layers 3109 with a
thickness of 70 nm and a negative electrode 3110 with a thickness
of 300 nm are formed by vapor deposition. In this embodiment, the
EL layer 3109 has a configuration in which a hole injection layer
with a thickness of 20 nm and a light-emitting layer with a
thickness of 50 nm are stacked. Needless to say, another known
configuration may be used in which a hole-injection layer, a hole
transport layer, an electron transport layer, or an electron
injection layer are combined with a light-emitting layer.
As described above, an EL element 3111 composed of the pixel
electrode (positive electrode) 3106, the EL layer 3109, and the
negative electrode 3110 is obtained. In this embodiment, the EL
element 3111 functions as a light-emitting element.
Next, a substrate (hereinafter, referred to as a "sealing member")
3113 for fixing the devices is attached to the layered
configuration obtained as described above with a first adhesive
3112. In this embodiment, although an elastic plastic film is used
as the sealing member 3113, a glass substrate, a quartz substrate,
a plastic substrate, a silicon substrate, or a ceramic substrate
may be used. As the first adhesive 3112, it is required to use a
material that can allow the peeling layer 3102 to be selectively
removed later.
Typically, an insulating film made of resin can be used. In this
embodiment, although polyimide is used, acrylic resin, polyamide,
or epoxy resin may be used. If the adhesive 3112 is positioned on a
side of an observer (i.e., on a side of a user of an electrooptical
apparatus) seen from the EL elements, a material that transmits
light needs to be used.
The first adhesive 3112 can shut off the EL elements from the
atmosphere. This can substantially completely suppress the
degradation of an organic EL material due to oxidation, and the
reliability of the EL elements can be substantially enhanced.
Next, as shown in FIG. 19B, the peeling layer 3102 is removed,
whereby the device forming substrate 3101 and the insulating film
3103 are peeled off. In this embodiment, peeling is conducted by
exposing the peeling layer 3102 to gas containing halogen fluoride.
In this embodiment, chloride fluoride (ClF.sub.3) is used as
halogen fluoride, and nitrogen is used as diluted gas. As the
diluted gas, argon, helium, or neon may be used. The flow rate of
ClF.sub.3 and nitrogen may be set at 500 sccm (8.35.times.10.sup.-6
m.sup.3/s), and a reaction pressure thereof may be set at 1 to 10
Torr (1.3.times.10.sup.2 to 1.3.times.10.sup.3 Pa). Furthermore, a
treatment temperature may be a room temperature (typically,
20.degree. C. to 27.degree. C.).
In the above-mentioned case, although a silicon film is etched, a
plastic film, a glass substrate, a polyimide film, and a silicon
oxide film are not etched. More specifically, the peeling layer
3102 is selectively etched by being exposed of ClF.sub.3 gas, and
finally removed completely. The active layers of the photodiode
3104 and the EL driving TFT 3105 similarly formed of a silicon film
are covered with the first interlayer insulating film 3107.
Therefore, they are not exposed to ClF.sub.3 gas and hence, are not
etched.
In the case of this embodiment, the peeling layer 3102 is gradually
etched from exposed ends. When the peeling layer 3102 is removed
completely, the device forming substrate 3101 and the insulating
film 3103 are separated. At this time, the TFTs and EL elements
formed of stacked thin films remain on the side of the sealing
member 3113.
Herein, the peeling layer 3102 is etched from the ends thereof.
When the device forming substrate 3101 is increased in size, it
takes a longer time for the peeling layer 3102 to be completely
removed, which is not preferable. Thus, the peeling layer 3102 is
removed by etching, desirably when the device forming substrate
3101 has a size of 3 inches or less (preferably, one inch or less),
measured from the upper left corner to the lower right comer.
In this embodiment, the peeling layer 3102 is removed by etching in
an atmosphere of ClF.sub.3 gas. The present invention is not
limited thereto. It may also be possible that a laser beam is
radiated to the peeling layer 3102 from the device forming
substrate 3101 side to vaporize the peeling layer 3102, whereby the
device forming substrate 3101 is peeled off. In this case, it is
required to appropriately select the kind of a laser beam and the
material for the device forming substrate 3101 so that a laser beam
passes through the device forming substrate 3101. For example, when
a quartz substrate is used as the device forming substrate 3101, a
YAG laser (fundamental (1064 nm), second harmonic (532 nm), third
harmonic (355 nm), fourth harmonic (266 nm)) or an excimer laser
(wavelength: 308 nm) is used to form a line-shaped beam and the
line-shaped beam may be allowed to pass through the quartz
substrate. An excimer laser does not pass through a glass
substrate. Therefore, if a glass substrate is used as the device
forming substrate 3101, a fundamental, a second harmonic, and a
third harmonic of the YAG laser (preferably, the second harmonic
(wavelength: 532 nm)) is used to form a line-shaped beam, and the
line-shaped beam may be allowed to pass through a glass
substrate.
In the case of conducting peeling by using a laser beam, the
peeling layer 3102 that is vaporized with a laser beam to be
radiated is used.
In addition to the method of using a laser beam, it may also be
possible that the device forming substrate 3101 is peeled off by
dissolving the peeling layer 3102 in a solution. In this case, it
is preferable to use a solution that allows the peeling layer 3102
to be selectively dissolved.
When the TFTs and the EL elements are transferred to the sealing
member 3113, as shown in FIG. 19C, a second adhesive 3114 is
formed, and a second device forming substrate 3115 is attached. As
the second adhesive 3114, an insulating film made of resin
(typically, polyimide, acrylic resin, polyamide, or epoxy resin)
may be used. Alternatively, an inorganic insulating film
(typically, a silicon oxide film) may be used. In the case where
the second adhesive 3114 is positioned on an observer side, seen
from the EL elements, a material transmitting light needs to be
used.
As described above, the TFTs and the EL elements are transferred
from the device forming substrate 3101 to the second device forming
substrate 3115. Consequently, an EL display apparatus interposed
between the sealing member 3113 and the second device forming
substrate 3115 can be obtained. If the sealing member 3113 and the
second device forming substrate 3115 are made of the same material,
thermal expansion coefficients thereof become equal to each other.
Therefore, the apparatus becomes unlikely to be influenced by
stress distortion due to a change in temperature.
In the EL display apparatus produced in this embodiment, the
material for the sealing member 3113 and the second device forming
substrate 3115 can be selected without being influenced by heat
resistance during a process of TFTs. For example, a plastic
substrate can be used as the sealing member 3113 and the second
device forming substrate 3115, whereby a flexible EL display
apparatus can be created.
This embodiment can be carried out by being arbitrarily combined
with any of the configurations shown in Embodiments 1 to 8.
Embodiment 11
In this embodiment, the case will be described in which a DLC film
is formed over the entire surface of an EL display apparatus or at
ends of an EL display apparatus.
FIG. 20A is a cross-sectional view of an EL display apparatus in
which a DLC film is formed over the entire surface of the
apparatus. On a substrate 3201, a switching TFT 3205, an EL driving
TFT 3204, and a photodiode 3206 are formed. Reference numeral 3203
denotes an EL element. The EL driving TFT 3204 controls a current
flowing through the EL element 3203.
The switching TFT 3205, the EL driving TFT 3204, and the EL element
3203 are sealed with a sealing member 3202 and a sealant 3208 so as
to be shut off from outside air. Reference numeral 3209 denotes
drawing-around wiring. The drawing-around wiring 3209 extends
between the sealant 3208 and the substrate 3201, and is exposed to
the outside of the space in which the EL element 3203 is
sealed.
Reference numeral 3210 denotes a DLC film. The DLC film 3210 covers
the entire EL display apparatus, excluding a part of the
drawing-around wiring 3209 exposed to the outside of the space in
which the EL element 3203 is sealed.
In this embodiment, a DLC film may be formed by ECR plasma CVD, RF
plasma CVD, .mu.-wave plasma CVD, or sputtering. The DLC film has a
Raman spectrum distribution with an asymmetric peak at about 1550
cm.sup.-1 and a shoulder at about 1300 cm.sup.-1. The DLC film also
exhibits a hardness of 15 to 25 GPa, when measured by minute
hardness meter. Such a carbon film protects the surface of a
substrate. In particular, a plastic substrate is likely to be
damaged. Therefore, covering the surface of the apparatus with a
DLC film as shown in FIG. 20A is effective for preventing
damage.
The DLC film is also effective for preventing oxygen and water from
entering the space in which the EL element 3203 is sealed. Thus, by
forming the DLC film 3210 so as to cover the sealant 3208 as in
this embodiment, a material promoting the degradation of an EL
layer, such as moisture and oxygen, from outside can be prevented
from entering the space in which the EL element 3203 is sealed.
When the DLC film 3210 is formed, a part of the drawing-around
wiring 3209 exposed to the outside of the space in which the EL
element 3203 is sealed is covered with a resist mask or the like,
and the resist mask is removed after the DLC film 3210 is formed. A
part of the drawing-around wiring 3209 not covered with the DLC
film 3210 is connected to wiring 3212 for an FPC provided at an FPC
3211 via an anisotropic conductive film 3213.
FIG. 20B is a cross-sectional view of an EL display apparatus in
the case where a DLC film is formed at ends of the EL display
apparatus. On a substrate 3301, a switching TFT 3305, an EL driving
TFT 3304, and a photodiode 3306 are formed. Reference numeral 3303
denotes an EL element, and the EL driving TFT 3304 controls a
current flowing through an EL element 3303.
The switching TFT 3305, the EL driving TFT 3304, the photodiode
3306, and the EL element 3303 are sealed with a sealing member 3302
and a sealant 3308 so as to be shut off from outside air. Reference
numeral 3309 denotes drawing-around wiring. The drawing-around
wiring 3309 extends between the sealant 3308 and the substrate
3301, and the EL element 3303 is exposed to the outside of the
space in which the EL element 3303 is sealed.
Reference numeral 3310 denotes a DLC film. The DLC film 3310 is
formed so as to cover a part of the sealing member 3302, a part of
the substrate 3301, and the sealant 3308, excluding a part of the
drawing-around wiring 3309 exposed to the outside of the space in
which the EL element 3303 is sealed.
The DLC film 3310 is effective for preventing oxygen and water from
entering the space in which the EL element 3303 is sealed. Thus, by
forming the DLC film 3310 so as to cover the sealant 3308 as in
this embodiment, a material promoting the degradation of an EL
layer, such as moisture and oxygen, from outside can be prevented
from entering the space in which the EL element 3303 is sealed.
In an EL display apparatus shown in FIG. 20B, the DLC film 3310 is
formed only at ends (portions including the sealant) of the EL
display apparatus. Therefore, it is easy to form the DLC film
3310.
When the DLC film 3310 is formed, a part of the drawing-around
wiring 3309 exposed to the outside of the space in which the EL
element 3303 is sealed is covered with a resist mask or the like,
and the resist mask is removed after the DLC film 3310 is formed. A
part of the drawing-around wiring 3309 not covered with the DLC
film 3310 is connected to wiring 3312 for an FPC provided at an FPC
3311 via an anisotropic conductive film 3313.
This embodiment can be carried out by being arbitrarily combined
with any of the configurations shown in Embodiments 1 to 10.
Embodiment 12
As an exemplary area sensor of the present invention, a portable
hand scanner will be described with reference to FIGS. 21A and
21B.
FIG. 21A shows a portable hand scanner, which is composed of a body
401, a sensor portion 402, an upper cover 403, an external
connecting port 404, and operation switches 405. FIG. 21B shows a
state where the upper cover 403 of the portable hand scanner in
FIG. 21A is closed.
The area sensor of the present invention is capable of displaying a
read image on the sensor portion 402. Therefore, even if an
electronic display is not separately provided to the area sensor,
an image can be confirmed as soon as it is read.
The area sensor of the present invention is also capable of sending
an image signal read by the sensor portion 402 to electronic
equipment connected to the outer side of the portable hand scanner
through the external connecting port 404, whereby the image is
corrected, synthesized, edited, and the like on software.
This embodiment can be arbitrarily combined with any of Embodiments
1 to 11.
Embodiment 13
As an exemplary area sensor of the present invention, a portable
hand scanner different from that of Embodiment 12 will be described
with reference to FIG. 22.
Reference numeral 501 denotes a sensor substrate, 502 denotes a
sensor portion, 503 denotes a touch panel, and 504 denotes a touch
pen. The touch panel 503 has light transparency. Because of this,
the touch panel 503 can transmit light emitted from the sensor
portion 502 and light incident upon the sensor portion 502, and an
image on a subject can be read through the touch panel 503. In the
case where an image is displayed on the sensor portion 502, an
image on the sensor portion 502 can be seen through the touch panel
503.
When the touch pen 504 contacts the touch panel 503, information at
a position where the touch pen 504 is in contact with the touch
panel 503 can be captured in an area sensor as an electric signal.
As the touch panel 503 and the touch pen 504 used in this
embodiment, any known members can be used, as long as the touch
panel 503 has light transparency, and information at a position
where the touch pen 504 contacts the touch panel 503 can be
captured in an area sensor as an electric signal.
The area sensor of the present invention having the above-mentioned
configuration is capable of reading an image, displaying the read
image on the sensor portion 502, and writing to the captured image
with the touch pen 504. In the area sensor of the present
invention, read of an image, display of an image, write to an image
can be all conducted in the sensor portion 502. Thus, the size of
the area sensor can be minimized, and the area sensor is allowed to
have various functions.
This embodiment can be arbitrarily combined with any of Embodiments
1 to 12.
Embodiment 14
In this embodiment, a configuration of a sensor portion of an area
sensor will be described, which is different from that shown in
FIG. 1.
FIG. 24 shows a circuit diagram of a sensor portion of an area
sensor of this embodiment. A sensor portion 1001 is provided with
source signal lines S.sub.1 to S.sub.x, power supply lines V.sub.1
to V.sub.x, gate signal lines G.sub.1 to G.sub.y, reset gate signal
lines RG.sub.1 to RG.sub.y, sensor output lines SS.sub.1 to
SS.sub.x, and a sensor power source line VB.
The sensor portion 1001 has a plurality of pixels 1002. Each pixel
1002 includes one of the source signal liens S.sub.1 to S.sub.x,
one of power supply lines V.sub.1 to V.sub.x, one of gate signal
lines G.sub.1 to G.sub.y, one of reset gate signal lines RG.sub.1
to RG.sub.y, one of sensor output lines SS.sub.1 to S.sup.x, and
the sensor power source line VB.
The sensor output lines SS.sub.1 to SS.sub.x are respectively
connected to constant current power sources 1003.sub.--.sub.1 to
1003.sub.--.sub.x.
The pixel 1002 includes a switching TFT 1004, an EL driving TFT
1005, and an EL element 1006. In FIG. 24, although a capacitor 1007
is provided in the pixel 1002, the capacitor 1007 may not be
provided. The pixel 1002 further includes a reset TFT 1010, a
buffer TFT 1011, a selective TFT 1012, and a photodiode 1013.
The EL element 1006 is composed of a positive electrode, a negative
electrode, and an EL layer provided between the positive electrode
and the negative electrode. In the case where the positive
electrode is connected to a source region or a drain region of the
EL driving TFT 1005, the positive electrode functions as a pixel
electrode and the negative electrode functions as a counter
electrode. In contrast, in the case where the negative electrode is
connected to a source region or a drain region of the EL driving
TFT 1005, the positive electrode functions as a counter electrode
and the negative electrode functions as a pixel electrode.
A gate electrode of the switching TFT 1004 is connected to the gate
signal line (G.sub.1 to G.sub.y). One of a source region and a
drain region of the switching TFT 1004 is connected to the source
signal line (S.sub.1 to S.sub.x), and the other is connected to the
gate electrode of the EL driving TFT 1005.
One of the source region and the drain region of the EL driving TFT
1005 is connected to the power supply line (V.sub.1 to V.sub.x),
and the other is connected to the EL element 1006. The capacitor
1007 is provided so as to be connected to the gate electrode of the
EL driving TFT 1005 and the power supply line (V.sub.1 to
V.sub.x).
A gate electrode of the reset TFr 1010 is connected to the reset
gate signal line (RG.sub.1 to RG.sub.x). A source region of the
reset TFT 1010 is connected to the sensor power source line VB. The
sensor power source line VB is always kept at a constant electric
potential (reference potential). A drain region of the reset TFT
1010 is connected to the photodiode 1013 and a gate electrode of
the buffer TFT 1011.
Although not shown in the figure, the photodiode 1013 has an N-type
semiconductor layer, a P-type semiconductor layer, and a
photoelectric conversion layer provided between the N-type
semiconductor layer and the P-type semiconductor layer. The drain
region of the reset TFT 1010 is connected to either the P-type
semiconductor layer or the N-type semiconductor layer of the
photodiode 1013.
A drain region of the buffer TFT 1011 is connected to the sensor
power source line VB, and is always kept at a constant reference
potential. A source region of the buffer TFT 1011 is connected to a
source region or a drain region of the selective TFT 1012.
A gate electrode of the selective TFT 1012 is connected to the gate
signal line (G.sub.1 to G.sub.x). One of a source region and a
drain region of the selective TFT 1012 is connected to the source
region of the buffer TFT 1011 as described above, and the other is
connected to the sensor output line (SS.sub.1 to SS.sub.x). The
sensor output line (SS.sub.1 to SS.sub.x) is connected to the
constant current power source (103.sub.--.sub.1 to
103.sub.--.sub.x), and is always supplied with a constant
current.
In this embodiment, the polarity of the switching TFT 1004 is the
same as that of the selective TFT 1012. That is, when the switching
TFT 1004 is an N-channel type TFT, the selective TFT 1012 is also
an N-channel type TFT. When the switching TFT 1004 is a P-channel
type TFT, the selective TFT 1012 is also a P-channel type TFT.
Unlike the area sensor shown in FIG. 1, in the sensor portion of
the area sensor of this embodiment, a gate electrode of the
switching TFT 1004 and a gate electrode of the selective TFT 1012
are both connected to the gate signal lines (G.sub.1 to G.sub.x).
Therefore, in the case of the area sensor of this embodiment, the
length of a period during which the EL element 1006 of each pixel
emits light is the same as that of a sampling period (ST.sub.1 to
ST.sub.N). Because of the above-mentioned configuration, the number
of wirings can be decreased in the area sensor of this embodiment,
compared with the case shown in FIG. 1.
The area sensor of this embodiment is also capable of displaying an
image on the sensor portion 1001.
The configuration of this embodiment can be arbitrarily combined
with any of Embodiments 1 to 13.
Embodiment 15
Examples of electronic equipment using an area sensor of the
present invention include a video camera, a digital still camera, a
notebook computer, a portable information terminal (mobile
computer, mobile phone, portable game machine, electronic book,
etc.), and the like.
FIG. 25A shows a video camera, which includes a body 2101, a
display portion 2102, an image receiving portion 2103, an operation
key 2104, an external connecting port 2105, a shutter 2106 and the
like. The area sensor of the present invention can be applied to
the display portion 2102.
FIG. 25B shows a mobile computer, which includes a body 2301, a
display portion 2302, a switch 2303, operation keys 2304, an
infrared port 2305, and the like. The area sensor of the present
invention can be applied to the display portion 2302.
FIG. 25C shows a mobile phone, which includes a body 2701, a
housing 2702, a display portion 2703, a voice input portion 2704, a
voice output portion 2705, operation keys 2706, an external
connecting portion 2707, an antenna 2708, and the like. The area
sensor of the present invention can be applied to the display
portion 2703.
As described above, the application range of the present invention
is very large. Thus, the present invention can be used for
electronic equipment in various fields.
This embodiment can be arbitrarily combined with the embodiment,
and any of Embodiments 1 to 14.
According to the present invention, due to the above-mentioned
configuration, light is radiated uniformly to a subject, so that no
inconsistencies in lightness are caused in a read image.
Furthermore, unlike a conventional example, it is not required to
provide a backlight and a light scattering plate separately from a
sensor substrate. Therefore, the mechanical strength of an area
sensor is increased without requiring precise adjustment of the
position of a backlight, a light scattering plate, a sensor
substrate, and a subject. As a result, an area sensor can be made
small, thin, and light-weight.
The area sensor of the present invention is also capable of
displaying an image on a sensor portion, using EL elements.
Therefore, even if an electronic display is not separately provided
to the area sensor, an image read by the sensor portion can be
displayed on the sensor portion, and the read image can be
confirmed immediately.
Furthermore, in a photodiode used in the present invention, a
photoelectric conversion layer is made of an amorphous silicon
film, an N-type semiconductor layer is made of an N-type
polycrystalline silicon film, and a P-type semiconductor layer is
made of a P-type polycrystalline silicon film. The amorphous
silicon film is thicker than the polycrystalline silicon film, and
the ratio in thickness therebetween is preferably (1 to 10):1.
Since the amorphous silicon film is thicker than the
polycrystalline silicon film, the photoelectric conversion layer
can receive more light. According to the present invention, the
amorphous silicon film has a light absorptivity higher than that of
the polycrystalline silicon film and the like, so that an amorphous
silicon film is used for the photoelectric conversion layer.
Various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the scope
and spirit of this invention. Accordingly, it is not intended that
the scope of the claims appended hereto be limited to the
description as set forth herein, but rather that the claims be
broadly construed.
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